murray. he's got more variety, just as quick, better slice, better vollies, content to push at times and be patient when the situation warrants, unlike the hot and cold djokovic. due to murray's variety, he can beat you in many different ways depending on opponent's game, unlike djokovic, who is supersolid but much less multifaceted.
not sure why people are saying djokovic will be/is better on grass than murray. murray's slice, volleys, guile, quickness, serve, etc. translate perfectly to grass, whereas djokovic's volleys and slice are a tad suspect.
and as far as clay potential, i see murray having a more suitable game than djokovic, since he is patient, can push the ball, and has recently dedicated himself to becoming superfit, fitness being something djokovic needs to improve his "breathing problem" notwithstanding. also heard murray can bench 300, which ,if true, evidences his dedication to conditioning.
another thing is that i don't think people realize murray's change in court temperment/demeanor. sure he used to mope and whine, but towards the middle and end of '08, he seriously started limiting his negative emotions and exagerating his positive ones. he's even slightly confrontational on the court now, something that i think will help him keep focus.
just my 2 cents