Basically what a lot of other people said.
I'm going to come from a pugging perspective. (cause I don't have enough time, or consistant time to be able to get any meaningful groups going)
With my experience with mastering a couple lights, the Atlas, the Kit Fox, and watching other people playing Lights + assaults this is my view on them. Though do keep in mind, a lot of the time it depends on the individual mech.
Also, I think heavies are the easiest mechs to pilot in the game as they get the best of both worlds so they are never in a situation where they perform terribly (aka Jack of all trades). Mediums are are slightly harder, but that's only because they are just overall weaker versions (and sometimes faster, but sometimes they can be slower than heavies) of heavies in general (Stormcrow and other "top tier" mediums are exceptions to the rule).
Lights -
#1 Reflexes - Requires faster aiming, and knowing how to throw someone's aim off.
#2 Ability to switch up what type of gameplay you want to do immediately often - Lights do not have to worry as much about what the team is doing, or where the enemy is (but you still want to know a little bit, need to avoid getting 1 shotted by going around corners). However, lights need to learn how to switch to different jobs quickly. Whether it's scouting for your team so they know where to go (or LRMers to shoot), Assassinating someone out of position (Lights often search for weakened mechs to finish them off or at least disarm), Protecting that one assault that the rest of the team ditched so he can get back to the rest of the team, or just making the enemy team chase the "squirrel" (you), or just preventing other lights from doing their job, you have to be able to be able to keep these things in mind so you can swap to the appropriate task at the right time.
#3 Avoid standing still as much as possible. You never know when someone might be out of position looking to snipe you and you don't know it. I cannot tell you how many lights I've 1 shotted or legged just because they were standing on a point, or because they were using large lasers to poke at some of my teammates (though sometimes they try to do that with short range weapons too, Surprise, that person isn't alone!).
Assaults -
#1 Tactical Thinking - Requires more radar memorization of both the enemy AND allies more than any other mech. This is because you are going to have to react to what will happen long before it actually happens.
#2 Teamwork is required - You can dish out damage, and take it, but without a team to support you, it'll all be wasted. Knowing when to be the one to lead a push forward, or one to be a guardian to stop anyone that tries to bumrush, or to start moving before the rest of the team moves is something you need to keep in mind.
#3 Learn to use your shield arms, quite a few of the assaults have arms that are good for shielding, however, unlike mediums and heavies, they take a few seconds to turn, so you have to do this before the enemy shoots.
#4 Learn to use your weapons at the appropriate times, as many Assaults have more than 1 weapon system. Due to the increase of weapons, you'll generally have to be more careful with your heat as well.
Though, each one has a major flaw that keeps me away from them because they make those weight classes feel luck based:
Lights - All it takes is one good alpha to destroy you (and Clan Streak SRM 4s or 6s boats are your worst nightmare since you probably will not be able to outrange them as chances are you will be using Medium lasers or SRMs and they can just 1 shot you). Situational awareness can greatly reduce this risk of this happening, but there is no way to 100% prevent it from happening.
Assaults - You are most likely going to be left in the dust when your team goes forwards. Chances are you will never be able to catch up, so you will get killed because of this and there's nothing you can do about it. Chatting with your teammates is the only way to have any hope of stopping this. However, there are times where it's better for the team to leave you for dead, than to go into a terrible position to protect you.
So yeah, 2 different skillsets. Whichever one is harder, depends on where your skills as a player lies.
As for which one is harder for me, depends on what kind of mindset I go into the game with. Afterall, playing a MWO light feels like a completely different game compared to playing MWO with an Assault, which feels nothing like playing a Medium/heavy to me (but mediums and heavies feel very similar to me). The slow lights, are yet another thing that feels nothing like the 3 other styles of gameplay as well, as you're basically an escort/low threat level target that can wreak havoc if ignored.
I will say though, Kit Fox is one of the hardest mechs I've played, and it took me the longest time out of any mech to get used to playing it well though. Aggressive support is such a strange gameplay style.
Best performance I've seen an Adder do is in Canyon Network. Running the dual PPC setup. he got 1089 damage with 5 kills (all at the very end), and not a single player on either team got even half of that damage. He was almost untouched by damage outside of my ER large lasers on my kit fox touching him every now and then, but he kept hiding too quickly for the lasers to do even half of the duration (and I got distracted by other enemies with larger alphas).
Edited by Keeshu, 30 January 2015 - 11:12 AM.