First of all PLEASE don't vote unless you are well familiar with the work of both bands. i.e. don't vote for Zeppelin because you're a big fan of them but have only ever heard a few DP songs, or vice versa.
My vote goes to Deep Purple. I actually think they have it all over Zeppelin. I love Zeppelin's good songs but all in all I don't think their albums as a whole are that great, with the possible exception of IV. Deep Purple have a good 4 albums which are great right through. Both had awesome guitarists and vocalists, though Page would have an edge over Blackmore I think. Plant and Gillan are pretty much on par imo. I've never been too concerned with drummers or bass players so no comment there. Just watching a live Deep Purple dvd last night though, their keyboard player was also pretty awesome.
But in the end I just like DP's albums a lot better than Zeppelin's, and for that reason they get my vote.