Well just my 2 cents :

I think I would be pretty nifty to have a nation Frigate, mind you I'm not talking about a Uber FF, and I'm also not talking about a "planned FF". I'm saying it would be nice to have a nation FF that was real unlike other ships in this game (Graf 2, Montana, etc).

My personnal favourites
U.K / Canada - River Class (or instead of FF a Corvette)
USA - Tacoma Class
Germany - Geleitboot 1941 (although she was destroyed in the shipyard)
Japanese - couldn't find one (suggestions ?)