I'm a first-year law student at ASU, but I'm also 28 and don't hang with the undergrad crowd at all, so take that for what it's worth.
For undergrad, Arizona is considered the "better" academic school of the two, although neither has much of a national reputation in that department. There are some very,very bright students at both, but admission requirements and tuition are so low for in-state students that there are a ton of morons around that hurt the reps of the schools. I don't know too much about Arizona except that my friends that have visited both are much more partial to Tempe than Tucson.
People here often say that ASU is just hurt by its "Party School" rep, but I went to undergrad at a "Party School" and we've always been highly-regarded when it comes to academic. They just let in too many in-state kids with bad scores and overall the school suffers. It does have a good business school and strong Law and MBA programs. There are a few other good programs, but that's all I really know.
I have almost zero interaction with undergrads or the "college lifestyle" anymore, so I can't help you much on that end but I can say that there is plenty to do around Tempe. Although purely from a "scenery" point of view, the few times I have wandered through the main campus, there is quite a bit to look at! And having come from the upper midwest myself, the weather is certainly a strong selling point.
