I've done all 3. None of them is hard. Tam is the easiest because of the shorter length. At 2600 feet, Mt. Tam is only slightly taller than popular peninsula climbs like Tunitas Creek or Kings Mountain or Page Mill Road.
Diablo is a little steeper than Hamilton, but Hamilton is 20 miles of climbing, which can wear you out if you don't pace yourself.
I assume you're talking about the San Jose side of Mt. Hamilton. The back side is steeper, but with substantially less elevation gain since it does not go down to sea level. You can do both sides for a good workout.