I usually pick a couple of guys that seem to learn quickly when you spar them and are not good fighters and just make them trainers. Look at Hibram Paz on my roster for instance. He is my sambo trainer. Once I figured out that he wasn't a good fighter I only trained him in Sambo. Now everyone on my roster that needs to train Sambo trains with him at a much faster rate, because his sambo is so high. Same with Henry Jenkins and wrestling, etc.

For now I would decide on a style or two that you really like, so that you can aim to develop your fighters that way in the future. They're all equally effective so it's just a matter of taste. It's a lot easier to mold your fighters to your camp's chosen style, whatever it ends up being. You'll have better equipment more suited to train certain styles, and your current fighters will have higher stats to train the future ones with.