None of these are really good choices, other than Lyn, and maybe Krom, but I'd prefer Roy to return. Black Knight could work, but I just don't see it. And why Sothe? His role in Path of Radiance was stupid.
The best choices would be Roy, Erika, Ephraim, Lyn, and maybe Krom.
Of course, I think it would be awesome to throw in a wyvern knight or a Pegasus knight in there, it's just hard to find one character major enough to put in there.