Freestyle Wrestler & BJJ
In my opinion Brazilian Ju-Jitsu and Freestyle wrestling work the best. Japanese Ju-Jitsu is great but it has some flaws and that is why Mitsuyo Maeda came to Brazil in the 20th century to help recreate Ju-Jitsu. He first introduced it to the Gracies clan and they have helped him re-make Ju-Jitsu to what it is today, Brazilian Ju-Jitsu. They tweaked it up and it has proven to work better than original Ju-Jitsu. Freestyle Wrestling is also great. Taking down opponents, sprawling, moving them around, etc. Overall it's great to learn. Every mixed martial artist nowadays should learn any type of Ju-Jitsu and Freestyle wrestling, then work on submissions specifically. Grappling is the 2nd key to success in a fight. Number 1 is standup, 2 is grappling, and 3 is finishing which is usually submissions.