The best place on the net for A/UX info is
www.aux-penelope.com (which is down at the moment, but you can read a lot from Google's cached pages if you need the info now).
I have A/UX 2.0 and 3.x.x, but so far have only ever run version 3. My main A/UX system is a Quadra 700. At some point I'll most likely set up my Mac IIcx or IIci so that I can run version 2.0.
Most of my documentation in the past has been Apple supplied manuals on version 3, but a friend just gave me a couple old book (one covering A/UX 1.1 and the other covering 2.0), so I've had a little more interest in exploring the older versions in the last few weeks. Sadly, I doubt I'll ever seen 1.x as Apple's main way of distributing A/UX back then was to sent people a hard drive with it pre-installed.
As for user experience, it is generally the same as running System 7.0.1 and the X apps are the same as if you ran them over a network on a Mac with MacX installed (because MacX is generally how you run X apps in A/UX).
I'd have to check, but as I recall A/UX 3.x.x came with MacX 1.1 and could be upgraded to 1.5. I know that you can't use MacX 2.0 on an A/UX system as it is PowerPC only.
One of the options lets you switch memory modes, letting you run System 6 apps. Though I haven't tried this yet, I've been considering it for playing with Macromind Director 2.0. Otherwise, I haven't used my Quadra 700 for much in the last few years as I have better systems for running most of my old apps.