Are you riding street or racing? If street DRZ. If racing RMZ.
Like Craig said above,the RMZ requires ALOT of maintenece. Frequent oil changes,valve checks, 4sp is horrible for street,and getting one street legal is not easy. If you find a newer one with close ratio 5sp. They are tough to properly gear for street riding too.
DRZ is street ready out of box. Oil changes every3k and valve checks every 12k. Sure they are down on power but the aftermarket is loaded with performance parts. If you buy wisely,you can get a loaded DRZ with all the goodies: pipe,carb,cams,& or big bore. You'll rebuild a RMZ 2-3 times before you wear out a clutch on a DRZ.....
There are Pros and cons to both. What are you willing to do?
Cheaper DRZ, perform better? What type of performance, as in what are you going to do with the bike? Some guys are quite content to own a tagged race bike if they don't ride much, and it's just a weekend toy. They have all week to change oil, check valves, etc. For me, I love turning wrenches on my stuff, but I love to ride more, so I bought a DRZ knowing full well what I was getting from the onset. And not once have I ever been dissapointed in my decision, I love my DRZ. Also, the service intervals in the manual are useless if you're actually riding the bike hard. I run quality full synthetic oil, and really good filters, and my oil is done at 1,000 miles. Since the engine oil is shared with the transmission, the DRZ has a built in oil change gauge, the shifter will tell you when it's time for a change. Listen to it, and you're bike will live a long happy life. I have 14,000 + miles on my bike, I run the dog shit out of it, no issues whatsoever. Best damn bike I've ever owned.