I'm going to surprise myself and go with the consensus here. In situations such as this, I always tend to give the edge to potential and given the fact that Snider could be keepable, I assumed I'd stop there and say drop Pena. However, looking more at your league structure, I don't see Snider becoming much better than a 15th round pick. He's had a resurgence lately, but a lot of that appears to be luck aided; his July numbers are propped up by a .388 babip and high for him fly ball %. Also concerning is that when he was in the minors, he did not hit like he had in the past and showed a surprising lack of pop. Even if Snider goes crazy and hits a perfect world .300 with 10 homers, his overall line is still going to be ugly and won't go in most drafts until the 10th to 13th round or so. Even in the perfect world scenario, he's unlikely to be a keeper.
Pena is a pain to own with that BA, but he is very productive and can give an excellent power boost when needed. He's certainly a great guy to have on the bench even if he doesn't have much upside.
Thanks for the help with mine.