We recently found ourselves going down this same path. We decided on the DR650. While I'm far from an expert rider, and don't want to fool you into thinking I know all, I can go over some of the highlights of this particular debate.
Seat height. The DRZ is high. Like ~38 inches high. I'm a six foot tall guy with a long inseam, and I thought it was a bit high... The DR is at about 35 in the high setting, 33 in low. Did you know there are two settings? Our dealer didn't. It's a fairly involved process to make the change (mostly the rebuilding of the front forks), but it can be done.
Air cooled vs. water cooled. Long standing debate. Pick your own side, but it is a major difference.
Highways. I don't know where you hail from, but if it's out west, I'm sure you already know that our highway speeds differ greatly from what you'll find on the other side of the Rockies. While neither one of us wants to go 90mph on a dualsport, we didn't want something that had nothing left to offer above 70mph either. Sometimes you need to get out of the way. There are also significant areas where the only way to get from here to there involves roads where traffic flows at 70mph and up, you don't want to have to run all out just to keep up.
Aftermarket support. The DR has a huge following, with offering of all sorts. Choices and competition are nice in the market place.
There are/were others, but those are a few to think about for right now. Now I'll shut up and let others with more knowledge chime in.