I went with DelPo.
DelPo is a strange player.
I try to see his matches whenever I can and see about half of them.
When DelPo plays I have a hard time figuring out how he wins.
He seems to move so slow and doesn't really hit the ball hard a lot of the time.
The serve is pretty good but not for someone as tall as he is, he should be using that height advantage more on the serve.
His endurance is lacking, at times he'll just get the ball back and many times he won't even run for balls that he can get to if he wants.
He just tries to conserve energy whenever he can.
My main gripe is his endurance, I've seen plenty of matches where he just isn't putting full effort in moving around the court.
When he does then he's drained for a few points.
There's no reason he can't be in top physical condition, if he can get this area in good shape like it was in 2009 he'll save himself a few sets before getting into the later stages of tournaments.
And when he gets to the final matches he'll not only have the extra endurance he worked for but less sets played on top of that.
I'm still waiting for prime Delpo.
One word: consistency.
Even on his worst days, JMDP is too consistent for the vast majority of the tour. He never beats himself, you have to beat him. It is not the same Del Potro who won a Slam and was about to break into the top 3 back in 2009/early 2010, but his consistent power is still too much to handle for all but a handful of players.