Without seeing the rest of your team I'd say Stay Put. You'd just be getting a downgrade at SS. Hamels and J. Upton are both primed for big years and are possible CY/MVP candidates. What does your pitching staff/OF look like.
It's a fair trade a little in your favor, but it depends on your team situation. All things being equal, getting hitting in return for pitching is advantageous because hitting is more consistent than pitching.
If your starting pitching is still good without Hamels, and you need OF help, its a great deal for you.
Upton replaces Castro's Stolen Bases Upton is better to have than Hamels. Unless... Is your starting pitching still good w/o Hamels? If no, then you cannot accept Is your OF weak?
If your OF is weak and you have at least 2 ace-quality SPs and at least 2 other good SPs, accept the trade.
If your OF is weak, but you dont have enough good SPs to do well in pitching categories, you cannot accept the trade because you wont be able to compete.
If your OF is NOT weak and you have enough good SPs w/o Hamels, it's up to you. Going hitter heavy is more advantageous than pitcher heavy unless there are injuries
If your OF is NOT weak and you DONT have enough good SPs w/o Hamels then DO NOT accept.
Its a 5 OF league, and I agree with you I need to think about it as I think J. Upton will be a monster this year. I liked the advice of adding a OF in exchange for an SP.
What do you think of this Hamels / S. Castro / Bourjos for J. Upton / Y. Escobar / B. McCarthy. I really don't want to throw in Mayberry, could be this year's M. Morse. I think Fowler's poor spring makes him not attractive enough for this trade right now.