Name Analysis: Their names both consist of two first names (David, Brent, Michael, Scott). Michael's middle name is Gary, so could it be David's middle name was Larry?
From what we've seen, Michael and David don't seem to actually do any work in the office.
Both pride themselves as "entertainers." Michael perhaps is more ambitious, attending an occasional acting class.

When the U.S. version first appeared, Michael Scott was David Brent's long-lost twin. However, as NBC series develops further, obviously to extend their storyline, Michael now has his owm personality, complete with his own irritating quirks and offensive comments. Both seem to have the same level of self-deluding sense of worth, importance and appeal to the ladies.

Fisticuffs: Although Michael's shown to be pretty good in the arena [US Ep. 206: The Fight], let's face it. David's got a few pounds on him. Plus, with all that he's gone through, I think he'd fight harder, since he doesn't seem to have that much left. If Michael was at an English Pub, he'd get a bit excited about those beers -- even if Mikey Boy had homecourt advantage at Chili's, he'd probably order a few two many Awesome Blossoms and go into food coma. Plus, didn't everyone see David's head butts [UK Ep.105: New Girl] his new secretary? He's vicious. Just vicious.
But in the Battle of Wits? David disappointed us on Quiz Night [UK Ep. 103: The Quiz]. And Michael surprised us all with his people skills and sly salesmanship getting a big account [US Ep. 207: The Client] at of course, Chili's - the new golf course, where business happens... as Small Businessman Magazine says (in the Letters to the Editor section).