I hope to know how selective they are (considering how strong applicants are as well).
In my opinion, strictly talking about admission difficulty and very roughly, there are 3 tiers in top 20:
tier 1: top 4
tier 2: UW Seattle, UIUC, Cornell, etc.
tier 3: UCLA, UCSD, etc.
Ranking-wise, it seems Princeton fits to tier 2 and Harvard fits to tier 3, but since they have really small department, I wonder whether the admission difficulty will be higher than (bigger) schools in the same tier? I know this is a rather dumb question, but need some info to choose reach / safety school stuff...