I'm going to list all of the "bad" 'mechs that I have. It should be noted that I have a similar interest to the OP and I have found builds that work rather well on all of these chassis, with the exception of the Vindicator which is, as far as I can tell, nearly irredeemable even though I have managed to find a build that does kind of okay. Let's begin. Note that these are not in any particular order and I have mastered all of them.
Locust: This was my first 'mech. I love it. People count it out because it's only 20 tons and is the most fragile 'mech in the game. That being said, I nab plenty of kills with this baby with 6 medium lasers and a beam duration quirk that makes that 30 points of damage nearly pinpoint.
Awesome: People say this 'mech is bad because it has weak armor for an assault 'mech while also being huge as far as geometry, hitboxes, and sheer size go. This was my first assault 'mech, however, and I still use it to this day in FW because I perform so well in my 8Q with a max standard engine, 2 PPCs, 2 ER Large Lasers, and 3 Medium Lasers.
Kit Fox: This 'mech is considered bad simply because it is as fragile as a light 'mech but not fast enough to really dodge fire like other light 'mechs. That being said, if you treat the thing like a fragile medium 'mech instead of trying to play it like a light you can accomplish some pretty cool things in it. I run mine with 4 Medium Pulse Lasers and 2 Machine Guns, also using the leg omnipods that have Jump Jets.
Commando: This 'mech is considered bad basically because of hardpoint starvation. It simply does not have the hardpoints or tonnage that it needs to give it a real serious alpha strike, and alpha strikes are the name of the game right now. That being said, I do very well in my Commando 1B with max XL engine, 3 medium lasers, and 1 SRM6. Doesn't sound like much, but it should also be noted that the Commando is at the moment the fastest 'mech available in the game and before the speed tweak nerf actually maxed out at the game's "speed limit" where HSR supposedly gets broken.
Vindicator: This is the only 'mech on this list that I actually agree with the general consensus of it just being bad. It has bad hardpoints, is too easy to hit, and is far too fragile. It boils down to this 'mech being too large and slow to dodge fire but not durable enough to tank the damage that it can't dodge either. I had an awful time in mine while trying to run it with PPCs and it was the only 'mech in this list that I had a negative KDR with. It was bad. Eventually I managed to rescue its KDR by doing something very strange with it: A 1AA with maximum XL engine, 4 Medium Pulse Lasers, and 1 LRM15.
Adder: Unpopular for the same reason that the Kit Fox is unpopular. I have found, however, that the Adder is a very good ERPPC platform if you play it right and is one of the rare instances where the stock loadout just about got it right. I run a pretty much stock Adder Prime. The only change I have made to it is when they unlocked the flamer in the head I replaced it with an ER Small Laser. This means that my Adder sports 2 ERPPCs and 1 ER Small Laser.
Mist Lynx: The drawback of this little guy is the fact that it simply does not have the tonnage or harpoints to carry any real serious alpha strike potential. If you want ECM on it you have to sacrifice half of your already meager weaponry. Its weapons are only found in its arms regardless of what omnipod combination you use and its arms are lost very easily in combat. That being said, I do pretty well using the Mist Lynx as a backstabber light 'mech with 4 Small Pulse Lasers. People also say that the Mist Lynx is slow, but I have personally found it to be fast enough to play it like I would any other light striker.
Urbanmech: People think this 'mech is bad because... well.. it's an Urbamech. It's supposed to be bad. Even in lore. But it's actually not. It rolls damage quite well thanks to the 360 torso twist and completely round body and can pack a pretty good punch in energy weaponry. I run an R60L that does pretty darn good sporting the largest XL engine the thing can carry and is armed with 4 Medium Pulse Lasers and 2 Machine Guns.
Spider: This 'mech is considered bad because of its hardpoints. There is not a single variant of this 'mech that has the hardpoints to pack a serious alpha strike. That being said, I do well in my 5D with ECM and 3 Medium Pulse Lasers. I play it pretty much the same way I play my Commando since they both have similar loadouts and speed,
Panther: This one is considered bad because people say that it's slow. Personally, while it is not as fast as other IS lights, I find it to be fast enough to perform just like any other light. I run a 9R with 4 Medium Pulse Lasers and 1 SRM6.
Gargoyle: I'm honestly not certain why everyone hates this 'mech. I do great in it. It is extremely fast and responsive for an assault 'mech and can outrun a lot of IS heavies. This is the only assault 'mech that I have ever piloted that I felt safe going lone wolf for a little bit because it's just so speedy that if I get into trouble have the speed neccesary to back out and return to my team. I run 2 Large Pulse Lasers and 4 ER Small Lasers. I get kills galore with this setup.
Summoner: It's not difficult to see why people don't like this 'mech. Again, this is a case of hardpoint starvation. The most energy hardpoints you can squeeze out of this 'mech at once if 4, which is quite honestly pathetic for a clan heavy 'mech. That doesn't keep me from enjoying and doing well in mine, however, loaded with 4 Medium Pulse Lasers and 1 LRM20.
Ice Ferret: This is another one of those 'mechs that I don't quite understand why everyone hates. I do extremely well in it. It's like the Clan Cicada. I run my Cicada with 6 Medium Lasers on IS and with the Ice Ferret I do almost the same thing with 5 ER Medium Lasers. It plays almost identically to my Cicada.
Shadow Cat: Again, this one is yet another case of hardpoint starvation. The most energy harpoints you can get out of this 'mech at one time is 3. I used to run mine with 2 Large Pulse Lasers and 1 ER Medium Laser. It was tolerable, barely. Later I switched some omnipods around and came up with 3 SRM6 and 2 ER Medium Lasers. It does very well at splatting things and getting you out of harms way quickly if you utilize its MASC properly.
Crab: Yet another 'mech that is very unpopular for a reason that I do not comprehend. I do so well in my Crab that I bring it as my medium 'mech to FW. It's very tanky and rolls damage extremely well. If you're moving, you're a rather difficult target to kill. This thing is fast, well above 100 KPH with a maximum engine, and has enough energy hardpoints to be absolutely lethal and still manages to be heat efficient. I run a 27B with max XL engine and 6 Medium Pulse Lasers.
Catapult: This 'mech is basically unpopular because it is too big for its own good yet its armor is too weak to justify being such a large target. It's certainly a difficult 'mech to run, but I do pretty well in my C4 with a standard engine of a size that I cannot remember, armed with 4 SRM6+ARTEMIS and 2 Medium Lasers.
Victor: Ah, the Victor. The Victor used to be meta. It used to be the king of the poptarts. Then we got hoverjets from PGI's balancing department, poptarting became a thing of the past, and so did the Victor. The fact of the matter is that the Victor is poorly armored for an Assault 'mech, and does not have the tonnage to bring any really serious firepower without bringing in an XL engine which just makes it even more vulnerable because the thing is hardly XL friendly. I had a real hard time with this 'mech but eventually found a build that performed well for me. You're gonna laugh. You're not gonna believe me when I tell you what build I use. You're going to think I'm insane, but trust me, I have a 2.0 KDR with this Victor. I run a 9B with maximum XL engine and armed with 2 Medium Lasers, 2 SRM2, and 3 AC/2. What started out as a desperate "I'm grasping at straws" troll build actually turned out to be completely surprisingly effective.
Warhawk: I'm not real sure why people dislike this 'mech. I think it's just a symptom of the fact that it was released alongside the Dire Wolf and everyone thought that anything the Warhawk could do the Dire Wolf did it better. The Warhawk is one of my more recent additions to my 'mechbays and it's been a very welcome one. I see a lot of people turning their Warhawks into LRM boats. Please don't do that. This 'mech can offer a lot of direct fire support while also tanking a fair amount of damage. I run mine with 2 ERPPCs and 2 Large Pulse Lasers. I love it.
Kintaro: The Kintaro. Overlooked and forgotten. The Kintaro isn't really a bad 'mech, but it's just that there are other 'mechs that can do what the Kintaro does better, thus people have just started calling the Kintaro a bad 'mech and never playing it. I had success in mine with SRMs and LRMs. The final build that I ended up settling on was pretty close to the Champion Kintaro build. I run my Kintaro 18 with 5 LRM5 and 2 Medium Lasers. Most people think that this is a troll build, but in actuality the LRM5s have less spread than larger LRM launchers and hit with almost pinpoint damage. So firing 5 of those puppies at once translates into 25 damage to you target's CT whereas firing two LRM20s would inflict roughly 30 damage to your target but spread out all over the enemy 'mech, thus being largely ineffective compared to concentrated LRM5 volleys. This Kintaro even runs cool enough that you can alpha strike the LRM5s all day long, completely ignoring their ghost heat penatly.
Archer: The Archer is in a bit of a sad state. It has poor geometry, is rather fragile, and is too large and slow to avoid fire and LRMs are pretty sub-par weapon systems in the current state that they are in, and LRMs are what the Archer is supposed to do. I couldn't do anything with the variants that had energy hardpoints, but I am pretty happy with my 5W which sports 5 LRM5 just like my Kintaro in the torsos and then 4 SRM4 in the arms, making me a deadly combatant at any range. I would suggest always running a Standard engine in an Archer. Their side torsos go pretty easy.
Dragon: The Dragon is overlooked simply because it has bad hardpoints. There's not a whole lot you can do with it. Even I, the guy who prides himself on finding uses for 'mechs that are largely considered useless, had to fall back to what used to be the Dragon's meta just to make a Dragon that worked at all. A 1N with 2 AC/5, 2 Medium Lasers, and 2 SSRM2. I don't remember what size of engine I have in it, but it's an XL. This 'mech isn't one of my favorites, but it works. If you don't feel like you need the SSRM2s to chase away light 'mechs then you can drop them to make room for a larger engine or something.
And that's all I've got. I hope this wall of text is helpful to somebody. At the very least, writing it entertained me for a while while I wait for the clock to let me go home on this lazy Friday evening.
Edited by Mole, 06 May 2016 - 01:34 PM.