I've been constantly asked this question by a lot of improvisers that I've met from the classes I take. First off, this may change in the future as I finish the programs but I think I have the gyst of what I think the differences are, but this is only my opinion but I think every school has its pro's and con's.
My current status is: Currently in Level 6 at Magnet, Taking 401 with UCB, and I'm in Pit Improv 401. For musical improv, I may do another one on those, that would be more in my musical improv blog.
Ask yourself these questions
How new am I?
If you are a seasoned improviser, UCB may be a great starter. I believe UCB is probably the hardest of all three of the schools because they are very specific about what they want. Game is key and you kind of need to be comfortable with improv to do it. I believe that as far as level 2, it is somewhat confusing for even experienced improvisers.
If you are new to improv, Magnet and PIT may be better fits. Magnet really focuses on the character portion or maybe the slower organic feel of improv. Everything you do is pretty much okay, this program will produce people who are comfortable on stage doing big characters. PIT is a very freeing and fun form of improv mostly based on relationships and knowing who you are to the scene. You will find more active players, aggressive yet fun. I find that though Magnet creates characters, some PIT may create comedic people. This is all conjecture ofcourse and my opinion.
What is your END GAME? This means what do you want out of it.
If you want fame, fortune, an SNL audition, or something to pad your resume as an actor, UCB is the path, but you will find the competition ridiculous. The good thing about that is that you will be taught by people who are great, on tv, famous even. UCB has a big payoff for the select few who rise to the top. Though there is no guarantee, and it may be equally as important to join the UCB sketch teams.
If you want to perform, then PIT is the winner for you. PIT has twice as many stages as Magnet, is open for longer periods of time. It also has a LOT of house teams, not to mention Keith Huang is probably the coolest guy and consistently offers people slots for shows. If you have an idea and you want to put it up, you could probably do it at PIT. They are probably the most supportive of their students. Though there is competition, it is far less than UCB and the talent is definitely there.
Magnet is kind of the wildcard here. I'd like to say if you want to learn improv for the sake of improv, I'd probably get beat on by all my friends in the other schools. I personally have found some amazing teachers and improvisers at the magnet. Unfortunately, it is kind of hard to get on stage at the Magnet, even as an indie team. I'd liken it to a person who wants to immerse yourself into improv, the Magnet Intensive are the most bang for the buck. It was impossible for me to pass up the 1-3 intensive.
What type of improviser are you?
If you're a character improviser, then Magnet is great for that. They encourage the use of characters, the feel of a scene, the feel of a physicality. That type of crazy character is loved at Magnet. Though that's not to say that it isn't at other places, let's just say that you may be more likely to find crazy stuff happening at the Magnet classes. Magnet is supportive in that way, in that you're not doing anything wrong.
If you're a comedian or a funny person in general, PIT may be for you. I've worked with lots of comedians and storytellers at the PIT. It seems that they thrive there. The storytelling shows, one person shows, stand up comedy shows, lends itself to funny people coming to the PIT. I like to think that the median improviser is funnier at the PIT, just because funnier people are there.
If you're a writer, sketch person, or old school improviser, UCB may be for you. It is very analytical and logical in the way it is taught. A writer would enjoy that, they realize the usefulness of improv in writing. Even when you watch class shows at UCB you may see people doing a lot of thinking. That's not hesitating, that's just thoughtfulness. Hopefully, by the upper levels, the thoughts come quicker and it's just fun. You may also find shows that are very talky but AMAZING. That's a great writer in there.
Competition for Teams?
House Teams: UCB= Ridiculously Competitive , I believe 500 for a few slots
Magnet: Competitive for different reasons. They only teach maybe 4 level 6's a year and there are less and less House team slots. So, if you get on a level 6, sometimes the pool is like 5 spots on teams. So, it's just harder by way of the system itself. Not as hard at UCB but harder than PIT.
PIT House Teams are competitive but there are LOTS of slots. They mix up teams, they add teams, subtract teams, add players, subtract players. Sometimes they have mixer ish teams (musical). Not to mention 10,000 hours which plays at the PIT has 3-4 teams that perform 2 times a month which is a type of house team. (I performed on a 10k team as well). There is no guarantee of getting on a PIT team, there is fierce competition but just by the numbers it is easier than Magnet and much easier than UCB.
Quality of Improv?
Who knows? I've got favorite teams. My favorite team now is Boss at the Magnet, but that is a slow type of improv that I don't see much of nowadays. The UCB form that's very gamy and writery can be the funniest thing I've ever seen. Asscats is classic in so many ways. They are awesome. PIT, you'll get old school teams like BBC or Baldwins. They get the job done and have an amazing time doing it.
They are all great improv schools. I would suggest going to see THE TEACHERS. They are your link to what you want to do. If you see a guy and say, I want to learn from that guy, go to that class. You're going to listen to someone more who you respect and enjoy.
That's it for today.