Don't mean to be rude but if you do a search on your topic all your questions have been asked & answerd many many times.
So what I am wondering are:
1. what are the main differences between them. "Short and sweet": Judo has many throws/take downs from the standing position. Depending on the dojo, little ground work and not much striking vs the other arts. Although watching a skilled Judo practitioner is something to see....beautiful techniques. Judo complimented with some of the striking arts is a nice compliment after a solid basic foundation.
"Traditional Japanese Jujitsu" has many take downs, throws, locks, kicks, punches and submission. More in the line of "karate". The grappling style Jujitsu that has become extremely popular is mostly all ground work, locks and submissions, lot of rolling around as you see on the UFC style fights, take a look at BJJ (Brazillian Jujitsu) The young bucks seem to like the BJJ and ground work, me I'm a kicker and puncher, don't like rolling that much.
2. How are they with street self defense. "All MA's are good" for SD, it's a matter of how long you train and your personal ability. Judo can be very nasty, depends how someone want to end a technique, ground surface, and the over all talent of the person being attacked.(That goes for all the arts) I have seen people train for years that couldn't defend themselves in a real situation but they love the art & work out which keeps them training. On the other hand I know guys that join our dojo and in a few months they are competing in MMA tournament kicking As*(^%. Personally I think the art is irrelavant, there all pretty good. The biggest factor is a person being able to apply what they have learned in a real life situation.
3. Which has a large competitive field? Well, that's a vast question since there are many types of Jujitsu. As you know grappling & MMA are the hot spots right now in MA. Judo is very big as well so they both hold many competition.
4. Also when looking for schools what are some key things to look for? Not going deep into the contract thing since everyone has their own opinion. But I will say as an instructor I like them since it keep a person coming on a regular basis. We offer non contract training as well and the turn over rate is much larger since they can drop out at any time or take off for long periods of time without financial guilt....enough of that. I'm not a big fan of people who join MA just to loose wait or get a summer work out, if a person wants to do that, go join a gym or one of those Billy Banks Dojo's
. Their mind set really isn't on MA from the begining. Sound stupid but try to get a dojo that has Air Conditioning, don't laugh there are two in our direct area that don't. I'm no sissy
(I think)but when it's 99 degrees outside the dojo is like an oven when everyone starts sweating. Do they have a changing room or do you have to get dressed at home, do they offer to train in the day & night? Can you train 5 days a week or are you on a certain type schedule?
The instructors: Does the Sensei,Shihan,Hanshi teach or sit back in his offic chair and watch a 16 year old BB try to run class, again I see you smiling but I see these dojo's at times. Come in and watch a class "with out" an appointment. Many times if your expected the mirrors will be polished if you know what I'm talking about. The average dojo price is about $100-150 per month. Watch a few classes, make sure you ask for a free week to see if your really at the correct dojo that's for you. Never new a owner to turn down anyone for a free week either. Look at how many senior student are in class. A good dojo should have some seniors that have been there for a while vs just a bunch of your kids, turn over. These are just some thing off the top of my head , I'm sure other poster can add to the list......good luck!