no musician is THE best.
There are greats..
not everyone will agree on who those are.. it only matters what you personally think.
I have been a DT fan for a long time and like their stuff.. My tastes have changed over time and I don't listen to them all that much any more (metal in general), but those guys are insane musicians (I'm a guitarist and Petrucci has been one of my bigger influences).
They are all very technically proficient.
I also like melody and feel.. This is something that this band gets slammed on against all of the time and I don't buy it. I've heard some very cool melodic stuff from them.. It all comes down to styles and what does it for an individual.. If he does.. great.. if not.. well.. why waste time arguing about it??
Something else.. Portnoy IS that band in terms of running and promoting it.
He's not just a drummer.
You can't really measure something like creativity or musicianship.. THANKFULLY..
There's always someone better ;)
I'm not a drummer, but my personal favs are Gavin Harrison, Dennis Chambers, Matt Chamberlain, Vinnie Colaiuta, Ian Mosley, Nick D'Virgilio, Mark Zonder, Mike Portnoy (he's a blast to watch)