I've got 'em both, a 2002 E53 with 136K an a 2009 E70 with about 60K. Both are 3.0s. The E53 with Sport Package is definitely more athletic - you sense no really less weight, but the wheelbase seems shorter, which makes it feel a bit more nimble. But the things that go wrong on the E53 just never seem to stop. The E70 needed an AC recharge and the fuel pump connector overheated, letting raw gas accumulate on top of the pump, but that's really it. It was fixed under the extended warranty (bought it this Feb.) but it really pissed me off that BMW could care less about a dangerous defect. I know, I talked to them. The E70 definitely comes across as more luxurious and has a very well finished interior, more of a luxo cruiser. I'm sure the M series doesn't come across that way!

My BMW dealer claims the E70s are pretty reliable, FWIW. I should have asked him what he thought of the E53; if he would have said the same thing, I would have known he was blowing smoke.

The E53 may not be around much longer. My wife wants to trade it for a lease on a Tiguan.