For me it's between J Upton and Kershaw.
I'm not interested in Mauer as you already have Posey.
As for your 2B backup should Utley get injured again, I'd look for a guy like Walker later in the draft.
Choo is rock-solid, but J Upton's ceiling is much, much, higher.
Given that you have C, 1B, 2B, OF, SP, SP kept, I would target J Upton. Snagging Kershaw would give you a brutal 1-2-3 of Kershaw, Hamels, and Jimenez, but with the other two already locked down you can afford to target some SP3s later on (Nolasco, B Anderson, T Lilly, etc..).
J Upton is a proven talent and still very young, hitting in a nice ballpark, and with more confidence. I'd draft him first.