In my opinion, the SN DD is the best for GB purposes; it has a sizeable number of T-slots, allowing the most useful employment of 'both' torpedoes (fore) and depth charges (aft). What's more, her aft-most T-slots can launch directly astern - greatly reducing the chance of being damaged by your own depth charges (as they are already behind you, rather than abreast, when you launch).
As per blitz, I'd have to second the vote(s) for Jaguar - especially if you don't get your gunners a few levels ahead of your operator through missions, etc.. At level 12, France is the only nation that offers a 5-inch single; allowing a properly played, level 12 crewed Jaguar to pummel level 12 crewed ships of other nations.