Been to Medellin multiple times now, have not been to the other choices you've mentioned. Also have been to Cartagena a few times as well, during my trips to Medellin, would suggest a 2 week trip and spend a couple of nights in Cartagena since it's a short flight from there.
If you're going to Medellin, stay around the El Poblado area, so you won't be to far from Parque lleras, since that's where the action is. It's fun for a little while, but after a bit, you'll probably wanna find someone to chill with instead of looking for a new girl every night. Also it helps to know some of the language, my first few trips I had to rely on translator apps and my friend to talk. Most if not all girls use Whatsapp and have a translator app, but it gets annoying to use after a while. This goes for day to day activity as well, such as site seeing/directions and restaurants. Also lots of Venezuelan beggars around, sad to see but it gets annoying as some are a bit aggressive (if you sit on the outside of a restaurant they will bother you).
As for Cartagena, a good majority of the women there are very good looking, you'll definitely want to stay there a few nights.
Also download Bumble, another way to meet providers, if you don't feel like hunting.