Updated: Jul 23, 2021
When choosing what type of grappling style to study or what type of gym to go to, you'll hear all kinds of things. "BJJ is best" or "Sambo beats all the other styles." When in reality, it's all about context. Why do you want to start training? Are you wanting to just pickup some self defense? Are you training for a upcoming fight and know your opponent is mean with ground and pound? These are the variables that will discern what discipline you want to train in.
Sambo and BJJ are probably the broadest of the grappling styles, they encompass everything from takedowns to submissions. They teach different things at different ranks like most BJJ white belts don't get to learn heel-hooks while newbies to Sambo are often taught that very early. Regardless both styles give you a very broad introduction and study of grappling. So if you want to just learn general self defense, these are tow good styles to study.
10th Planet Jiujitsu is a no-gi system. Meaning they don't wear the white karate uniform with the belt. Jiujitsu without the gi is give and take. Practicing without a gi lets you move faster and experience a more realistic simulation of an actual fight or encounter on the street. Practicing with a gi however, slows you down to make you more technical while honing your grip strength with thick cloth to grab translating to better holds in wrists and such. 10th Planet is a fun system, many of the worlds best Jiujitsu practitioners hail from 10th planet gyms.
Greco Roman Wrestling is ideal for takedowns, and takedown defense. If you want to focus on those two things, or be the type of fighter that opts in for ground n pound versus submissions. This would be a discipline you'd want to study. A good wrestler can maintain dominant position over a grappler and subdue them with strikes, we see it all the time in MMA. so if you're more of a striker than a grappler, Greco Roman Wrestling is the way to go.
Your best route as a amateur or pro fighter is to be well rounded and train accordingly for who you fight against, preparing for their strengths/weaknesses. Commit a little time to all of these styles but focus on what's best to prepare for your opponent. If you just want general self defense, find the best camp. I've seen gyms like a ex Hollywood stuntman who teaches all disciplines, but he was a stuntman not an expert in any style. You'd probably rather go to a gym with more experienced instructors in their disciplines for self defense.
So it's not always the style but equally the instructor to consider, and be sure to ask how they feel about you cross training. Old school camps don't like that, they want you only training with them. Many of those camps still yield top performing fighters. Newer gyms actually promote cross training and want you to learn as much from others as possible. Just make sure that gyms narrative fits how you want to train as well.