Cool, I've had all three. I've stuck with the N73 right now because of bad experiences with both the E70 and N80 that, I honestly believe outweigh wifi and/or a keyboard on the devices. The N80 had terrible battery life, recorded disgusting video, and took sub-par photos for a 3.2mp camera, when you would manage to stay still long enough to take them. I've reviewed the E70, which you can find in my sig. My main compaint was that the reception was terrible, and it appears to be that way even with the 850 variant, E70-2. The E70 also suffers from an additional lack of RAM when using the QWERTY keyboard.
I haven't had any problems with my N73, shy of accidentally bricking it with NSU and having to send it in to be revived. Solid phone overall and you really get the most for your buck.