A guy whose baseball opinion I greatly respect had this to say during an ESPN Insider chat today about the Uptons.
Odie (Portland): No question the Upton brothers are good. I just don't see a point in having this debate, because Justin is still so green. Sure, he's got the scouting reports, and he has the minor league track record, but all that major league success that's being thrown his way is pure conjecture. That being said I'd gladly take either of them. How would you rate the Upton boys compared to some other scary good power/speed guys out there? Matt Kemp, Chris Young, Nick Markakis?
Keith Law: Kemp is the only one of those three guys who could hang with the Uptons on tools. I think I'd still rank him third, just because I think the Uptons show a better feel for the game (Kemp was a basketball star in HS, so he's developing a bit late as a baseball player), but I think all three will be superstars.