You really only need a 4x2, I went through Hurricane George in Mayaguez (1998) and a 4x4 wouldn't have made any difference. Save your money and buy a generator (we were out of power for 5 weeks).
Crime is a serious problem even in Mayaguez, check out the mall parking lot and see security guards positioned on poles/guard posts. Keeping this in mind, I had more theft problems in nice communities in the States, than I had in Puerto Rico. I've lived in Condado, Mayaguez, Cabo Rojo and finally in a gated community in Humacao. You will notice many houses will have bars on their doors and windows, if you can live in a gated community (Mayaguez doesn't have any) your better off, or move further toward Cabo Rojo & Boqueron you will be OK. Just use common sense, and at night be careful where you go (i.e. go to dinner at the Mayaguez Casino (not the Holiday Inn) and then go straight home.
If you have children, that's a complete different story - seriously look at home scholling.