I would go with Muay Thai if you want a traditional art, it's one of the most effective and easiest to learn traditional styles. Otherwise I'd find a mixed martial arts gym (such as a Jeet Kune Do gym or generic MMA) and focus on finding one that teaches in a manner that you like. Watch a few classes and make sure the energy level is where you want it to be, that they spar often (in higher classes that should be every class), etc...
Those gyms generally teach multiple styles and allow you to gain rank in each style seperately if you wish. My gym (a Jeet Kune Do gym) teaches a mixture of Muay Thai, Savate (French kickboxing), Jun Fan Gung Fu, Brazilian Jui Jitsui and Kali/Silat.
The biggest change for you will be focusing more on the hand-work and ground skills as well as the Muay Thai kicks. You'll have to get used to turning your hips/body into the kicks instead of snapping each kick TKD style. Jun Fan and Savate both use TKD style kicking though (though they don't do all the kicks TKD does, the ones they do do match TKD). These are the issues I noted while training with a 13 year veteran TKD black-belt that just joined our program (and I've had a couple months of TKD myself long ago).
If you're just looking for a good work-out then look for a cardio kick-boxing program or get into Capoeira. Capoeira isn't all that useful compared to Muay Thai or MMA but it's a hell of a workout and looks very cool.
Those gyms generally teach multiple styles and allow you to gain rank in each style seperately if you wish. My gym (a Jeet Kune Do gym) teaches a mixture of Muay Thai, Savate (French kickboxing), Jun Fan Gung Fu, Brazilian Jui Jitsui and Kali/Silat.
The biggest change for you will be focusing more on the hand-work and ground skills as well as the Muay Thai kicks. You'll have to get used to turning your hips/body into the kicks instead of snapping each kick TKD style. Jun Fan and Savate both use TKD style kicking though (though they don't do all the kicks TKD does, the ones they do do match TKD). These are the issues I noted while training with a 13 year veteran TKD black-belt that just joined our program (and I've had a couple months of TKD myself long ago).
If you're just looking for a good work-out then look for a cardio kick-boxing program or get into Capoeira. Capoeira isn't all that useful compared to Muay Thai or MMA but it's a hell of a workout and looks very cool.