I just started playing last night and am looking to buy my first mech, but I really can't decide! I'm assuming I should stick to buying either clan or inner sphere if I want to play the faction mode? How do you tell if a mech is clan or inner sphere when you are buying them? I've played mechwarrior before so I know some of them, but there are a lot that I am not familiar with.
Light
Adder, Arctic Cheetah, Kit Fox, Mist Lynx
Medium
Ice Ferret, Nova, Shadow Cat, Stormcrow
Heavy
Ebon Jaguar, Hellbringer, Mad Dog, Summoner, Timber Wolf
Assault
Dire Wolf, Executioner, Gargoyle, Warhawk
The clan mechs were introduced after launch, so only the mechlab (and not the store) differentiates between IS and Clanner mechs. But yeah, it's best to stick with one at the start. Clan mechs were OP when they launched (and were P2W for a while), but they got hit with the nerf bat and IS mechs were buffed, both with the quirk system. Hover your cursor over a mech in the shop; most clan mechs only have negative gameplay quirks and a minor exp boost, while IS mechs generally have a long list of positive quirks (which also generally align with the hardpoints on IS mechs, so ferex a model that's set up to be a good LRM boat will have missile-related quirks.
If you're looking for advice on what to buy,
here is a good list of regularly updated tier lists, and
here is a guide for buying mechs for organized team play. I'll give a general summary as well:
1. Start with a set of three light 'mechs. They're cheaper initial investments and you'll need some to fill out the fourth spot on your lance when you play CW/faction play. If you want to go IS, either the Ravens or the Firestarters are good buys. If you want to be a Clanboy, get the Arctic Cheaters. Firestarters are the dominant IS light for classic "run around constantly being an annoying circle-strafing asshole" play, Ravens are no-competition the best support/sniper lights in the game. Arctic Cheaters are Firestarters except with ECM. My experience is with Ravens, here's how they break down:
3L: Best sniper in the game. No competition. Comes with ECM; strap on two ERLLas, unlock the module for extended ERLLas range and do constant poke damage from as far as ~1500 meters out. Equip the best(?) XL engine in the game at the same time so that you can run away at 150km/h.
4X: -30% laser duration, +30% laser range, but with no ECM. This is an excellent platform for 2x LPLas, because their firing cycle is reduced to almost nothing, so you can peek nothing but your upper right corner for ~1 second, drop your 22 damage alpha onto a single point, and be back in cover before they know they've been hit.
2X: I don't really like it, but it's a laser boat that can hit above its weight class. Has lots of quirks for making lasers more effective, and you can fit it with 2x LLas and 2x MLas, then alpha those for 28 damage or rotate them while being nearly heat-neutral.
Huginn: Premium, but it's an obscenely nasty SRM boat.
2. Remember, you need at least three variants of a mech to be able to get the Elite and Master skills for it. Master your light variants, sell any you don't enjoy/do well with, and start working towards an Assault or Heavy.
If you're going Clan, the Dire Wolf, Timber Wolf, and Ebon Jaguar are all very good. In CW that's pretty much all you'll see the Clanboys pulling. If IS is more your speed, you have more options, but the Stalkers, Battlemasters, Banshees, and Quickdraws generally have the most good variants. IS also has some exceptionally good premiums if you're willing to drop real money: I got two of the best, the Misery (which combines the super-troll hitboxes and zombie potential of all Stalker variants with the 2x PPC + AC/20 "40" build that will ruin anyone's day at any range) and the Ilya Muromets (which is still excellent despite brawlers and ballistic mechs being somewhat off-meta). The Stalker line in particular is worth pursuing: Misery as above is super-trolly if you torso twist and use cover well, the 4N is one of the best laser-vomit mechs in the game, the 5M is a superb LRM boat, and each of the 5S, 3H, and 3F are also good or above average laser boats or generalists, mostly thanks (again) to the high weapon mounts and hitboxes.
3. For filling things out, or if you want to grind trial mechs more before making your initial buy, there are good mediums as well. The Stormcrows, even post-nerf, are obscene. The Blackjacks are likewise exceptional.
Basically for CW it doesn't matter what you pick beyond personal preference, because outcomes are wholly derived from the matchmaking: groups beat PuGs 99% of the time; PuG vs PuG is a coinflip, though defense usually wins because it's easier for a bunch of idiots to camp a base than organize an effective attack.
So I've been having a look at this. How's the grind? Compared to, say, WoT?
Trivial. I got my first set of three 'mechs almost fully kitted out and with all skills elited in ~50 combined matches between the three, maybe, and have also finished almost all the basic skills and reoutfitting of the mechs I bought with real money, plus another Heavy I picked up with C-bills. The only real limiting factor is that mechbays cost ~$1.30 each, but you can get close to a dozen by running short contracts and playing 2-3 matches for each faction in CW, and you can also get gold currency &c. from the weekend challenges and higher CW rewards. I think that if you played a single faction in CW up to the top rank you'd have, what, 3 free mechbays and enough MC to buy 10 more? And of course once you've mastered a set of variants you can sell off the ones you don't like or use to make room.
By the by. Pilot skills/modules. The only mech modules worth getting are the one that instantly drops enemy radar lock when you move into concealment and the seismic sensor one. Don't waste GEXP on any of the others, use it for weapon modules instead.