The tanks with 4 howies and 2 snipes seem to still be really popular. Other than that, you have your sniper with grenade mix, your cannon with grenade mix, straight cannon mech monsters called sidewinders, due to their offset cannons on the side and then of course you have the triple singles that devastate you if you get in too close.
The city maps are still dominated by nothing but grenadiers. Hate fucking grenades, wish they would nerf the fuck out of them.
The AR mechs have seemed to die off, hardly ever run into those fuckers anymore, but once in awhile someone will pop up with a good one and kick my ass.
The game does seem to be experiencing a revival of sorts. You can generally find missions in the war for 2 to 5 players pretty easily and there seem to be more noobish to average people playing rather than the elite squads of the past.