Thanks for your help on mine.
A lot depends on how you project the keepers for the rest of the league and how long you can keep players for. That said, I would take Price and Jennings for the following reasons:
1) PEDs. I personally don't think MLB will have enough evidence to suspend Gio, but that's just my uninformed opinion. Either way, he has more risk.
2) Price is a true ace and that is hard to come by in a large keeper league. There aren't 16 aces out there, so it's a very valuable commodity.
3) You have enough BA in Castro and Posey to offset the BA risk you take with Jennings (or if you stick with Granderson).
4) You lose power by giving up Granderson, but you gain speed with Jennings. I think it will be easier to get power in the draft than it will be to get speed. Plus, it's not like Jennings has no power. I think he will hit more HRs than Granderson will steal bases. In fact, it's completely possible that Jenning will have more combined SBs+HRs than Granderson will.
5) Price, Gio and Jennings are still growing. Granderson has likely hit his ceiling and though he may have another 2-4 years of solid R/HR/RBI, I think you get more long-term keeper value out of Jennings and Price.