Since you've already started BJJ, I'll just make a few observations.
First, as has been mentioned, it's the instructor. Learning the proper technique will stay with you forever. Learning a "lesser than" technique may eventually cause injuries.
Pick a practice that suits your existing physical traits, that you can build on.
Short stocky = a natural grappling physique. Tall, lean and flexible, maybe a good kicking physique. (There's great kickers who are short and great grapplers who are tall.) You probably already know what direction you will gravitate towards based on who you are.
BJJ is an excellent discipline, but most of it's practiced techniques require a partner.
If you're a little flexible, but would like to become more so, TaeKwonDo or kickboxing would be great for that. Since TKD is taught as a "yes sir" discipline, it's probably not what you're looking for, but learning how to kick and the overall balance needed to perform kicks, helps you with everything physical. You'll walk better.
Once you learn proper punching and kicking techniques, you can go anywhere that has a heavy bag and get a great workout for the rest of you life - no need to join any schools long term, or always be looking for a partner.
Kicking burns a lot of calories!
I practiced TKD for decades and use bags today for my dry land training. Ten 3 minute rounds kicking and punching - best workout ever IMO.
This kid credits me with making him work out to exhaustion for the first time in his life. He signed up at our school when he was a teenager and we trained hard for competition.
http://youtu.be/Zs4uQ6DfKV8 Here he demonstrates a technique exactly how we were taught.
Our trainers were the coach and captain of the USA Olympic TKD team.
Again, it's all about the instructors!
It's funny how a new activity can change your life. I never intended to compete, I was just bored running ten miles a day and wanted a good workout. After a few years of perfecting my technique, I was curious to see how effective it was and fell in love with the team camaraderie.
Good luck, take it slow and have fun. Anything that makes you a better person is worthwhile.
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