I'll DM either. I'd prefer 4e.
And to let you in on a secret, I'd prep 3.5 very much like I'd prep 4e.
I'm now actually curious how a 4e monster would do against 3.5 PCs, with some minor adjusting and appropriate leveling. 4th level 3.5 PCs vs 1st level 4e monsters?
I have been doing that for a while now in a couple of my 3.5 games, a homebrew and The Red Hand adventure. It works quite well. I give them their bloodie hit points and watch their abilities, but otherwise play them as written, I have had no problems.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.