I think that Mexico and Costa Rica have such different vibes. Especially if you're talking about Los Cabos vs. Arenal/La Fortuna or Guanacaste area.
Mexico areas will have white sand beaches and sometimes sargassum. Costa Rica will not.
You can visit more 'inland' near the volcano in Costa Rica and have an amazing experience that doesn't involve a beach.
So, I really think it depends on what you want out of the vacation. If you're wanting a beach and all-inclusive resort I would lean towards Mexico.
I have been to both destinations and have felt safe every time I have visited.
I was in Mexico 3 times last year and I am going to Costa Rica in June.
Favorite properties in Costa Rica:
Amor Arenal
Tabacon
Nayara Springs
Secrets Papagayo
Westin Reserva Conchal
Mexico has so many that are great... Secrets Maroma is at the top as is Le Blanc, La Casa de la Playa and Excellence Playa Mujeres. There are even some amazing non-all inclusive like Nizuc, Belmond Maroma, and the Mayakoba area.
Lauren K '07
www.breezecustomtravel.com
@breezecustomtravel