I was able to play the game for real from 1987 to 1993, so I don't play DW like most people.

I started out on one of the last US diesel boats in Japan and then went to a 688 in Hawaii. So, for basic goofing around I'll stick with the 688(i) or I'll play around with the Japanese diesel boat (Japan based their real boat off the boat I was on) but its also fun to drive a 637 class or one of the "red team" subs.
I've been thinking of a way to express this, with RA the platform you choose almost doesn't matter. There is no singular advantage but all platforms have their own disadvantage(s). So, find a class of sub or ship that interests you and give it a try.
What's great about DW, there isn't one "right" way to play the game.