Depends on what state in the U.S. (assuming you're in the U.S.) you're in. Muay Thai will emphasize more on clinching, knee strikes, and low kicks than American Kickboxing. Elbows and knee strikes to the head will depend on what state you are in, what league you fight in, and if you're pro/amatuear/smoker level. But also it depends on the schools. I've seen Muay Thai schools that were pretty soft, and i've seen some pretty tough American Kickboxing rules fighters. However going to a good Muay Thai gym partnered with Western Boxing would be a better combo than an American Kickboxing gym and Western Boxing, but if you train hard either would be fine. What are you training for? Competing/fitness/self defense/etc?