Honestly, I would think a legendary founder would be able to answer that question better than I can. After all, the rest of us are even newer than that.
Anyway, I am happy to tell you what I've already done. This is pretty much my own opinion and preferences, so feel free to do your own thing if you want.
Lights:
The two light mechs I currently have in my stable is the
RVN-3L and
SDR-5D. Yes, two ECM mechs, as I consider them very important to the survival of the team as a whole. Actually, since the stat reset, my Raven has the best win/loss record of my entire stable with 18 wins 12 losses, in spite having the worst kill/death ratio with 7 kills and 18 deaths. Yes, I'm pretty sure that information warfare and supporting the team, even in pickup groups, works.
The Spider is lots of fun since it is the only mech out there with both ECM and jump jets. My record with this mech as of this writing is 17 wins, 13 losses, 19 kills, and 15 deaths. So it performs very well for me in spite the really low firepower rating. Mastering it was more of a hassle though, as trying to do anything with just an ER large laser in the center torso is really difficult (whether the 5V or the 5K). But I'm pretty happy with the final result.
Mediums:
What I currently have kept in this category is the
CDA-3M, and a couple of Wolverines (WVR-6R, and
WVR-7K). Unfortunately, my Cicada got hit really hard with the light autocannon nerf. But the combination of low-heat Ultra/5 fire with the two medium lasers allows it to DPS much better than my light ECM mechs. So it's still a keeper.
The Wolverines are an unusual choice. To be honest, my first mech mastery was reach with the Centurion series. Way back in the day the medium mechs either felt like overweight lights (Cicada) or underweight heavies (Hunchback), with the CN9-D the only one with the engine capacity and weight to actually feel like a medium mech to me. That has (obviously) been corrected a long time ago. But the Wolverine series looked like a perfect opportunity to put jump jets on my CN9-D loadout with enough variations in the other mechs variants to keep things interesting. Honestly, considering the loadouts that do work for me, I can't help but wonder if I wouldn't have been happier in a Griffin.
Although I personally don't like the fact that the big shoulder cannons block half your view, a lot of people like the Shadowhawk a lot more than the old Hunchback. Jump jets are a huge help with mobility and the Shadowhawk doesn't have that gargantuan "shoot here!" hunch that gave the Hunchback its name.
Heavies:
The top of my list here is the
JM6-S Jagermech. Since the stat wipe, this mech has the same 18/12 win-loss ratio my Raven has, but with a lot more impressive kill/death. Specifically 29 kills and 16 deaths. Very ironically, the autocannon nerf that has practically spelled the end of some of my medium designs doesn't seem to be slowing this beast down at all. For training and a change of pace, the
JM6-A makes a passable LRM boat.
I also have two of the Cataphracts still in my mech bays, including a
4 AC/5 CTF-4X, and a
2 AC/10 jumping CTF-3D. They have both been doing good for me with 18 winds 14 losses each. But honestly the low arms compared to the Jagermech series does make the Cataphracts feel awkward in comparison.
Assaults:
AS7-D-DC hands down is my first choice. (Or maybe
this one?) As the only mech over 40 tons to be able to carry an ECM, it really stands out. Unfortunately a bit too much, as any enemy DDC is my top priority for NARCing when possible. But I can say it's still fun to be in one, and seeing several at once on a time is a sure sign that somebody is going to have a really bad day.
But to be honest, I've been getting good results from two of the Highlanders, the
HGN-733C and
HGN-733P. The 733C is very close to being a "meta" build, and really good at winning (18 wins 14 losses). The 733P does spectacularly well as a missile boat (17 wins 16 losses).
Since I did talk a lot about some of my personal stats, I think I should say this. My
overall stats since the stat wipe are 243 wins, 234 losses (1.04 W/L), 295 kills, and 330 deaths (0.89 K/D). So I feel I'm very likely a mere average player. So, seeing good results on a specific chasis does say something positive to me about that chasis or the loadout I put on there. Your own mileage may vary.