-Wacos is a troll clan and shouldn't be joined unless you are willing to sell yourself away into slavery into sevices of the Wacos.
WACOS IS LUV
Anyhow, leaving some corrections on Ox's stuff:
Juggernauts - some really interesting templates, I don't know too much but they have loads of really active RP players, a good strategic community, and lots of really nice people in a close-knit community
They are a bit lacking on game frequency, but their forums one of the most fun in warlight (probably the best since the wolves' implosion), with lots of fun little games such as Mafia. Definetely a good pick.
Wolves - a really good efficient leader, a really active, thriving community (albeit somewhat toxic) that has really frequent games, an active chat game, and an active forum.
Kinda. Knyte is doing a good job "strategizing" the wolves up the ranks. The RP side of the wolves is decaying faster than Ion Antonescu's brain did. Save from a few really great names left (notably McMuller, [WOLF] Navigator and [WOLF]Andrew), you'll either get inactive people or straight up toxic people for diplos. Their strat side is growing similarly to AOE/EIC - a couple players (notably Semicedevine), while the rest are a shitpile that never get better at either thing and are a great suggestion to avoid contact with.
AOE - less active than usual and their diplo community is eroding a little, but they are always worth checking out because they're always improving
AOE's community is a bit weird and I'd place it somewhere in the line of worth and not worth. The players are friendly and growing strategically, but their diplomacy side never grew to be big, and up to this day is rather unreliable and eroding further. If your goal is a liberal, open community, AOE is a go. but if you're looking for actual roleplay, I'd suggest otherwise. They do have Sun Luna, which is one of the best ones of the website, and a couple other goodies (notably Wombat and Apollo), but wombat is appearently dead (like, really, dead; long story, he had a condition), Apollo moved his main out and Luna is having his RP games on a different account.
USSR - activity is pretty huge here, with good template creators. As inactive players are removed and new ones constantly recruited, it's a good place to make new friends, and play some really nice diplos
The average warlighter underrates them. They are pretty solid. Ox puts it well. But if you're looking into more fluidity and talking to communities off the clan, then this can backfire (they are quite closed).
rp - A really nice close-knit community with a lot of high-intensity role play. Games are quite infrequent, and they're somewhat isolated, but when they do make games, they're damn good.
RP, on the other hand, is a bit overrated. They do have some of the most committed roleplayers in the website, but game frequency is at best disappointing, and they care far too much about reputation (when reputation is as important as fun, something is wrong). They share USSR's major problem of isolation, too. I'd advise joining only if you actually plan on hosting games yourself.
EIC - quite an active community but it seems like a slightly worse version of AOE.
They are essentially the same as AOE, except slightly less welcoming, but with a slightly more alive roleplaying side (and generally more skilled) with some sacrifice on the strat side.
The Circle - They have damn good diplomacy games if you can stand their community. I personally love them but they're not very likable if you find them toxic.
This one is a hit or miss. Active players willing to join games all the time. But their way to play the game is questionable. If you like them, they're great. If you don't, you'll have a terrible time. Some of them are among my favorite warlighters to invite for a match (notably Leo Alexander).
League of Nations - not very active but their players get invited to games if you get yourself known in the diplomacy community
United Nations - trying to build themselves up right now
Nearly no players in there ever. The ones that actually are - and are active - are a 10/10 (see: FrancoPadini, Pablo Garcia)
After_Dark - Juq will invite you to Tactic games if you care, but idk if you do so probably not worth it
I don't think they are even RP anymore. Ollie does maps and an eventual game here and there. Juq joins a diplo every now and then and hosts loads of chat games and games with weird/unique rules. MGSB will accept all games you throw at him, but expect complaints about the government.
World League - if you want a management position in a clan that will be hijacked soon
Falcons - If you want to be the best in a clan this is the clan for you