Grappling Martial Arts

Im looking to add grappling skills to my current martial arts repertoire (Boxing, Kenpo(purple belt), Muay Thai). My striking and striking defense is very good, however aside from the clinch, I have no formal grappling training. I am currently considering bjj which is offered at my muay thai gym, sambo, or wrestling, but I am open to any suggestions. What are the pros/cons of each and/or which grappling style offers the best pairing with my current skill set.

(Note: For the purposes of competition.)