Brazilian Jiu-jitsu- Mostly mat work. They spend little time starting from standing, most sparring starts from the knees. This is the most ground intensive of just about all the arts. You'll learn transitions from all positions on your back or on the top, and submissions from the dominate positions. Arm locks and chokes are probably the most prevelant submissions used, but straight ankle locks, knee bars, and toe holds are all BJJ legal. One thing, though, is BJJ uses the Gi, which possibly could be uncomfortable at first coming from Muay Thai. Most schools do work no-gi, but it depends on the instructor. Honestly, I believe spending time in the gi is important training. Stand-up to mat work ratio is probably about 10% standing, and 90% mat work, but can varry depending on school.
Judo- Pretty much the same techniques as BJJ, but with a much greater emphasis on the standing portion of the match. Probably about 80% Stand-up grappling to 20% mat work. Again depends on the school. Like BJJ Judo is gi reliant, maybe moreso, if only because I see fewer Judoka practicing no-gi. Judoka stand up seems to put more emphasis on throws than say wrestling, and tend to fight from a more upright stance. On the ground legal submissions are only arm locks and chokes. There are no leg locks allowed. Judoka tend to be either more explosive on the ground due to stalling stand up rules, or they can stall for the stand up. Reffs stand judoka up if they feel there is no progress, which can be quite quick. Also judoka mat work includes wins by 25 second pins for the win, so like wrestling this can encourage turtling, or giving up your back (though, they often are good at defending their back too).
Other Jujitsu schools- It really depends here. Saying jujitsu is like saying Kung Fu. There are many different schools of Jujitsu and they differ widely. Some looking a lot like Judo, some looking more like Karate.
Wrestling- folk style or Free style wrestling are excellent grappling styles with great takedowns and strong top control on the mat. Their weakness is mostly submissions, and fighting from the back. Greco-roman wrestling has great take downs, but is all upper body.
Anyway, this is my experience as a BJJer, and I'm sure that those who have more experience in the other styles could add or correct me in those catagories.
