They really are two different animals completely. I loved both but for very different reasons.
If you are in the mood for a more tense, caustic family portrait ala August Osage County then go to see Other Desert Cities. It is superb but very dark and builds in its intensity.
If you prefer something very touching, humane, compassionate and at times hysterically funny then go for Sons of the Prophet.
If I could only choose one, I would probably pick Sons of the Prophet. The cast isn't as showy, but they are exceptional.
"The sexual energy between the mother and son really concerns me!"-random woman behind me at Next to Normal
"I want to meet him after and bang him!"-random woman who exposed her breasts at Rock of Ages, referring to James Carpinello