Medellin is literally one of my favorite cities on the planet so you so you can guess that women there are amazing. I was there for 3 weeks last September and literally felt like a hot chick by the end of my trip. I was actively turning down girls from Tinder and day game because I was swarmped with girls hitting me up .
Another great city is Warsaw, it is not as quite good as Medellin but I definitely has no shortage of girls there either . I haven't been to South East Asia, but from everything I heard it is like South America times a 1000.
In terms of STDs, I believe the HIV risk in South America is on par with US. As long as you are not hooking up with prostitutes or doing heroin, you have nothing to worry about .
Trannies on another hand are a ligit risk in pretty much all of S. America and S. East Asia.For some reason, I felt there are much more of them there than in US . However, if you use common sense you should be OK as well. One thing I always do is that if there is a tranny chance, I ask for the girl's height. If she is under 5'5" , the chance of her being tranny is low. If she is over 5'10" than there is definitly a real chance and if she is somewhere in the middle than you have to use your gut.

is this only South America?

I spent months in Indonesia (Bali and Jakarta). I loved this country for many reasons from the very friendly people to food to cost of living, etc. But for Tinder it is ridiculous good. It was like a buffet. Especially if you like 145-155 cm petite feminine women. Jakarta is too good. Bali has a lot of white girls and night game. But not exactly great for local women.
Budapest wasn't great for Tinder for me. But for night game was amazing. Day game as well.
Warsaw and Krakow is good for day, night and Tinder. Very nice country. Great cost of living.