Mobil 1 comes in 15W-50. I use this in the summer and would recommend this for you.
For winters in AZ, either their 5W-30 or 10W-30 should be fine. If you take the car on an overnight trip to the mountains I'd go with the 5W-30; otherwise use the 10W-30. Here in MN I use their 0W-30 but this may be overkill even in tundra country.