Depends upon what kind of Theme you want Bandejat.
Also, RP or not RP...?
Lady Arete on Unionhandbook
My Excel Badge tool
Well, as i'll create a new char the theme isn't important, i'm open to any theme. About RP or not RP i prefer RP
(edit. this info is based on the union server)
Well the New Heroes Union or the Vigilants are two that spring to mind...if it is RP based help you require the best people on the forums to contact would be;
@Ravenswing
@Floatingfatman
@Lady Arete
@Zortel
@Shadowghost
To name but a few, im a part time RP'r myself but nowhere near as accomplished as those above....but if it is simply a well established, fun and friendly SG, I could recommend our sg the "Art of War", in the top ten Union sg's, we run tf's regular arcs most evenings and there is a raft of old school players on who are happy to lend their time for anything you need.
Whichever route you take I hope you find what you need and have fun while doing it 
PM me ingame @stryke if you require any assistance 
(ps welcome to the forums 
)
Art of War Co-Leader - Union *Global@Warscythe*
"The box said Windows Vista or better - so I installed Linux"
Well speaking for New Heroes Union..
Well the New Heroes Union is one of the few RP (as much RP you can get) kind of sg's.
We have a few alternate dimensions or otherworlders in the sg, about half of our chars are lets say... like X-men or Avengers style.
Our supergroup channel is In char (we have an out of char channel for that talk)... Do take a look at this page for abit more about us.
Try us and if its something else you seek, then we can hopefully help you find that.
Lady Arete on Unionhandbook
My Excel Badge tool
Not really an RPer myself but I think NHU Supergroup is something I would also be interested in. I'll have to look you guys up when I am in game (15th-ish of December).
Now...To plan my character!
Is there any themed Supergroup recruiting? I'm new on these servers cause i used to play on USA ones. I'm looking for a cooperative supergroup.