This one is incredibly good/close, in all honesty, if you build a Clay deck and don't have both of these dudes you probably built it wrong.
So I guess I look at which one I'd splash first, and it's probably Barnabas.
However, Peter's heal is quite frankly amazing, and I'd much rather have him than Barnabas for most of the game, his enhancements are BONKERS. 4DC, TGT, he's just got to much.