As someone who has both here's what I think:

For everyday use: DZ is better
If you hack DZ: It's better still
If you will use the hacks (sudo ring any bells): The N900 is far better.

Basically get the N900 (only if you use it to its potential) otherwise get a better qwert-droid like the Captivate Glide, Droid4 or EPIC 4G (If you get CDMA).

Otherwise larger-droids like the Gnex and NOTE are sufficient enough to drop the physical keypad and slim down the device