Ellsbury's (healthy) downside is 50+ steals with an OBP hovering around Ichiro's batting average.
I used to really like Granderson until last year when I suddenly realized what an asshole he is. But his downside has also been his two year norm. If I had to pick the one who is more likely to take a step forward this year, I'd be more inclined to go with Ellsbury than Granderson.
None of which changes the fact that Ellsbury takes "Family Circus" routes on fly balls, throws like a crippled version of Johnny Damon, and is never going to have Granderson's power. But if Ellsbury can be a singles hitter with a .360 OBP instead of a singles hitter with a .330 OBP, I might give him the edge over Granderson. I don't think there's an obvious answer, though. They're different players, but both inconsistent players with high upside. Could go either (or neither) way.
EDIT: I hate to say this, but "what MPS2 said."
Edited by rominer, 22 December 2010 - 01:19 PM.