In terms of medical school itself, I would say Tucson. In terms of location, I would say Phoenix.
I would say the University of Arizona Tucson due to its long history. With medical schools, I am with the belief that it is generally safer to attend an institution that has more years of established rotations, experienced faculty, and a curriculum that has worked for decades. Tucson was established in 1965, while Phoenix was established in 2012. One thing to keep in mind is that the Creighton Phoenix medical school opened recently in Phoenix. If you prefer to be the only medical school in town, then Phoenix could be an issue 😉
I do not see many drawbacks with the Tucson medical school except the location (which matters a lot for the next 4 years). Phoenix is the capital of Arizona and is claimed to be the "economic, cultural and political heart of Arizona". Phoenix is also ranked in the top cities in Arizona, while Tucson is not even on the list from what I saw. From the articles I have read, Phoenix also has an NBA team, established restaurants, and a nightlife. In terms of lifestyle, you may enjoy Phoenix more if you are an outgoing individual. I have read though that Tucson also has nightlife, so you will also need to research into all of this.
It is hard to find the match lists of both schools. From quick searches, they both do very well at matching within Arizona and nearby states. Overall, it is up to you. You cannot go wrong with either choice since both schools are doing very well currently.