São Paulo, but you need to speak Portuguese otherwise you won't find the best offers. Other cities just can't be compared to São Paulo, almost unlimited amount of escorts, from models to uni girls.
São Paulo can be safe if you know the language, you'll find a lot of infos even online and how to avoid bad areas, but without speaking Portuguese you are limited to high-paid escorts because most girls won't speak English, you will have a very narrow group of escorts to choose from. Right now clinics are the best choice, every ''clinic'' has 10-15 girls and some new young girls appear from time to time, you just go to those clinics, chose who you want to fuck and pay. After becoming a good costumer they'll even send you pics from the new girls and offer them to you. Most girls come from different States, São Paulo is the biggest hub of escorts in the World in my opinion!