Tough choice, for all purposes Kendrick has almost everything you want from a prospect. He plays a weak position in 2B, is close to the majors, is very polished (he could stand to take a few more walks though), and looks to have .300 - 20/20 upside to him. If you need a 2B in the next year or so, he might be the better choice.
However, if you can wait and want the best prospect with the most potential, I think you have to go w/ Upton. Were not exactly sure at what rate or position he will stick, but we know for all reasonable circumstances that he will be pretty damn good. In other words it would take some bizarre event to keep him from becoming one of the best IMO.
I still question Drew and how good he will be, not to mention his work ethic and family lines. He tore up A ball, but struggled quite a bit in AA. Same goes with Wood, I'm not nearly sold on him yet as everyone else seems to be. There is no mistaking he has an amazingly good year last year, but something doesn't add up for me believing he is that good all of a sudden (who knows I may be wrong). He goes from being all glove and no bat to this? His BB/K #'s are basically the same so it doesn't seemed like he changed his style at the plate ... yet he hits 30 some more HR's and 20 more doubles? Lets just say if he keeps doing it, it won't matter in the end, but for now I'm not a true believer that he is indeed that good.