Building on Ltarget. I agree. Take a tour. There are great pilots and great mission planners in all countries. Dredger comes to mind for rooks, and Ghi, Falcon23, and 321bar for bishops(I'm biased since I fly Bish). Not sure about Knights haven't flown with them for a while. But I'm sure they have them. The most important aspect is which country displays good attitude. You don't want to be around quitters and whiners. However, we all whine at times.
In my experience I think Rooks have more pure fighters and Bish have more pure base takers and seem to be a little more stubborn about giving up a base than the rooks. The Knights seem to be a bit more hard nosed like the bish.
That's my humble opinion.
Enjoy the game and try all the planes and as many tactics as you can think of.