Is Puerto Rico a good place for a mainland American to travel and learn spanish?

Question

I have studied spanish both in college as well as in Mexico and now have a fairly conversant knowledge of the language, but there is still much more that I would like to learn of it. Is Puerto Rico a good place to perhaps attend a language school and practice the language with people there? What percentage of Puerto Ricans speak english, and do they tend to prefer to speak english or spanish with visiting mainland Americans? Also, how are visiting Americans normally viewed in Puerto Rico? Is there alot of anti-American sentiment there?

I know that each individual person in Puerto Rico is sure to have their own particular preference and opinion and thus I am not asking you to over-generalize, I am simply asking for the overall tendencies you have observed that one may encounter.

Thanks!