Mountainside fitness knows what a visit to the gym should be - clean, with great equipment, at a reasonable price.
Rumor has it that this location at Chase Field was actually for advertising. If you ever go, you'll notice that the membership is really low. Most of the time the gym is empty with maybe 5-10 people working out at any given time. It's great for members though because you never have trouble finding a machine or weights.
The equipment is all in excellent condition and they definitely keep the place really clean. It doesn't have a pool, basketball court, or racquetball - but it does have plenty of weight machines downstairs with cardio machines upstairs. I've never seen a class, but they do have them (just not a very robust schedule). I like to go at lunch since my work is nearby. The locker rooms are always clean (which is really important to me) and they provide clean towels as part of their standard membership.
And don't worry, the windows are covered so you won't be stared at like a fish tank if there is an event at Chase field.