Rio is the best in my opinion
I've been to many destinations including Southeast Asia, Europe and the Caribbean region. Brazil is hands down my favorite place for mongering. You can have great experiences anywhere, but on average Brazilian girls provide the most reliable GFEs. The sexuality of Brazilian women is impossible to put into words. Perhaps more importantly and without exaggeration, you will not find anything that compares to the Brazilian ass (Bunda! Some of the girls are thick, but even thin girls have posterior curves that kill. Brazilian girls are also all colors and sizes.
Rio is also one of the most beautiful cities in the world. The beaches also have the hottest women in the world. South Beach (Miami) is the only beach that can come close. Sure there are several mongering destinations that can be combined with beach holidays, but all in all I prefer a week chilling and relaxing on Copacabana or Ipanema beach combined with some sightseeing.
For mongers traveling alone, Rio can be a place to recruit a sex buddy / tour guide in a great tourist destination. This requires building some rapport. If you desire, some Brazilian "programa" girls are great at providing the allusion of a GF in and out of bed.
Lastly, I like the wide variety of outlets available for mongering. The Termas, Clinicas, Boates (like Barbarella), Escorts, Vila Mimosa, Avenida Atlantica bars and maybe even the beach. Everyone has their own preferred venues in Rio. I prefer the party atmosphere that can get going at a place like Termas 4 x 4. Currently, I am unaware of a dance club in Rio where you can reliably find working girls. We can hope though.