It's got a few more pixels.
Droid:854 x 480
Nexus: 800 x 480 pixels
I can't decide either, changing my mind every 5min. Droid now or wait x more days for N1...
That 54 pixels does help with some programs. It makes it easier to view a page sometimes without having to pan down more often. A small issue, but one non-the-less.
Here are some concerns with the N1 that have been addressed (in this thread) but, I will lay some out again.
AMOLED screen: Normally this isnt a issue, but this one has its fair share of touch screen issues with multi-touch and accuracy (its just how HTC builds them). And also with being INVISIBLE in sunlight. And over-saturation of oranges and reds.
Soft Keys: These have their fair share of issues (but so have many phones have). Hopefully the ATT or VZW version will have addressed these issues.
3G Issues: Even after a "fix" there are still many reports on 3G issues. But many have noticed that if you place your hand over the radio, it can cause it to go to Edge over 3G. Not a big deal, but if the radio isn't powerful enough to push through your hand, that can be problematic for some users. Again, hopefully the ATT and VZW version have addressed this.
Lack of a dedicated GPU: Now this is up for personal opinion. But if you want to play games on your phone or play around with that fancy FLASH when it hits our phones, that GPU is gonna make things a lot smoother!
A physical trackball: Sadly these little buggers have been a bane since RIM put it on their handhelds. Unless you play with your phone with rubber gloves on and in a vacuum, your trackball is gonna pull in dust and dead skin and such to the internals of the phone. Then you have to take it apart, and clean it all. But this can be personal opinion.....again.
Lack of a physical keyboard: This is big time personal opinion. And the soft-keyboard that Android has is fantastic! But it just isn't on par with a real keyboard.
Now the droid doesn't have that fancy snap dragon processor, but it isn't far off as far as benchmarks go. And you can always over-clock very safely.
But from reports I've seen the droid is far more reliable as a system. I mean, nearly 1.5 MILLION have sold since release. And you almost never hear wide-spread issues with it (unlike the N1).
Both are fantastic devices, but I would wait on the N1, let them work ALL the kinks out of it first.