I live in Phoenix and usually ride the WTB Veloceraptor (Raptor for short) it is an awsome all around tire. It is one of the most widely used tires ever produced.
It’s getting hot here now and I tend to migrate North into the mountains on the weekends and ride early mornings during the week down in the valley. When I head up north I switch to a Kenda Nevegal tire. This is another awsome "all around" tire and I think it handles the varying conditions a little better. I tend to hit more creek crossings, loose "deathdirt" mixed with some granite rocks, when I ride in Flagstaff. I would check with your LBS to see what the local buzz is for a good tire.
I seem to recall a nice article in Bike mag. or Mtn Bike mag (April Issue) regarding tires. It covered the different tire designs and gave a chart with tire suggestions for the different types of terrain that we encounter.