Hi Neal - I literally just went through this decision. In general I love and own a variety of Creed frags. I really wanted to wind up with Santal Imperial - it smells good, and if I am not mistaken is actually less expensive than other Creeds (at least according to the Creed Boutique website). My problem with it was twofold. First of all, while it smells good, it just doesn't have that much of a sandalwood scent. I was getting more of the ambergris. Secondly, the longevity is really just terrible. Usually that doesn't matter to me, as I often reapply, but this was just silly.
I really tested the MpG Santal Noble. It is definitely a "great one", but felt a bit "dirty" to me. Long story short - I just purchased Profumum Santalum AND Diptyque Tam Dao (couldn't make up my mind). The Profumum is really sandalwoody and creamier than the MpG, and I really just love it. I know you did not indicate you were considering these, but I think you should.
If your decision is absolutely between the two you mentioned, I would go with the MpG (the "dirtiness" notwithstanding).