Xavis off the ball movement and positional play is the best in the world by miles.
This is average xavi during a game, over about a minute (while almost always constantly moving, analyzing play and moving accordingly):
*glance left*
*glance right*
*jog a touch back into more space*
*glance over shoulder*
*glance right*
*glance at ball*
*glance at teammates/analyze play*
*glance right
while moving into a space after predicting 3 passes ahead, and realizing there will be a chance the holder of the ball might have less options than normal*
*while those 3 passes are happening glances left, the right, then left again, adjusts his position slightly, analyzes both opponents teammates positions and body language*
*glances left and right
as the ball is leaving teammates foot*
*quick glance at play again as he receives ball*
*controls ball (maybe shielding it from opponents as he does so*
*either,
a: decides to stick with pass he decided to go for 10secs/3 passes ago
b: quickly decides on different pass,
c: holds on to ball while reanalyzing play, patiently waiting
in all cases a, b and c, is already thinking about where to move to next, and where his teammates are likely to move to*
*makes pass, while
already moving to his chosen position. Begins to move the moment his foot touches ball. He'll move behind or between defenders, a few yards back, an open space, making himself available for a return or one-two etc*
*while moving into this space will be glancing left and right again*
*spends the nest bit of time he is not involved in play constantly moving, analyzing, glancing etc*
*is now sitting deep, but immediately moves forward into a well-chosen space to aid teammates when he deems necessary (usually if teammates havn't moved sufficiently to make themselves easy outlets for a pass)*
*and of course will be glancing around him as the ball is on its way to him, after he receives it and as he is making his pass.*
...all this in maybe 30 seconds to a minute. :O Seriously, just watch him constantly during a game- its amazing. And this is talking about his positional play and movement alone. Add to this the quality of his passing and link up play, his ability on the ball (particularly his shielding of the ball and little 360's) etc.
Atrociously underrated on the large scale of things due to his apparent subtly. I think he's the greatest CM of all time.