Oh My God is a satire on Indian’s nonsense traditions and rituals and shows us that if we apply some common sense, we can see easily the illogicality of those superstitions. It also shows that the mean people, whether it be the priests or the corporate fraternity, use those traditions only to make their profit and escape from their wrongdoings.
While 3 Idiots mocks our Education system for being too focused on the grading and marks rather being able to promote the individual to work towards enhancing their talents.
Both films are praiseworthy But we as Indians praise them for a while and a very few actually follows or care about applying them in real life.
I personally rate Oh My God better than 3 Idiots because when we will stop following the damn stupid rituals in our simple daily life, then only we can prevent the malaise (of following the herd foolishly even if its nonsense) from influencing is in other areas like Education system, politics etc.