Edit: I got beaten by a buncha other posts, lol. So listen to them, not me.
Please use the search function and/or trainworld next time.
Generally, it is believed KM has pwnage fighters and good DBers, UK has good TBers, US is
decent all around and has kickass CVs, and IJN... has lots of CVs. From what I've read in
forum threads.
Don't take my word for granted though, because I'm not a CV player. A better player can
answer your question more thoroughly.