I competed in one USDAA trial (and only one day, lol), so this isn't an expert opinion by any means. I agree with everything Ashley said. They are very lax about dogs on leashes, so lax, I was absolutely shocked. But then again, this is coming from a person who started in NADAC and they are very strict about leashes due to a very bad incident.
USDAA was very fun, very laid back atmosphere. The judge played music through the speaker box while we were walking the course or waiting for them to rebuild it. They have a lot of different games and tend to run about 3-5 runs per day (I think it's usually on the 5 side) of a trial. Ortegah was right about the jump heights. And when you do jump Performance, there's a few things I dislike about it, but I understand the reasoning for it. The A-frame is lower, they are no broad jumps and triples? Or something like that. They make it easier on the dogs to jump/climb, which is nice. Also, you don't get to do all the Championship games either. Performance has their own set. It just depends on what you want to do with it.
My dog is 17.5", he has to jump 22" in Championship in USDAA. I refuse to abuse his body like that, so I jump 16" in Performance. A woman who I train with, her dog jumps 8 and 12 in other venues, but 16 in Championship. Her dog is a Cavalier. I personally don't agree with her choice, but it's her dog.
Comparing that to AKC. AKC is a lot more "by the book". Their courses are tighter than USDAA, but this would depend on your dogs jumping style. Again, a woman I train with, her dog has a very long jump, she'll only run her dog in NADAC (which is even more open/flowy than USDAA). Another has a lot of issues in AKC because her dog jumps somewhat long even though her dog is small. AKC also runs 2 runs a day typically. They may add FAST or Time2Beat, but typically, you run Standard and JWW and that's it. The upside of that is your days are a lot shorter!
I started in NADAC. It's very different than most of the venues in that they don't use a lot of the equipment. IMHO, in order of fun, easy to get going, and payback rate (ease of Q'ing in the beginning) I'd rate them in this order: CPE, NADAC, USDAA, AKC (I haven't run anything else, so this is all I know). I probably wouldn't run my dog in AKC until it knows all the equipment very well. Koji was slow on contacts so we didn't start AKC until almost 9 months after trialing and at that, he sucked. lol. But, I'm also glad we didn't start AKC until later when he was also a lot more experienced.
Disclaimer: I haven't run the higher levels of CPE and USDAA so I'm not sure how those courses are. I'm just commenting on the lower levels of them all.
Last but not least.....money. CPE, NADAC, and USDAA run about 5 runs a day. Money can add up fast. BUT, at least their runs are $10-15 each. AKC runs about $20-25 for your first run of the day and $15-20 for any others that day. I started doing more AKC because although the runs are more expensive per run, by day, it's cheaper. I was spending about $120 for a weekend at NADAC. An upcoming USDAA in my area is about the same. Ditto with CPE. I believe all 3 venues give discounts if you run everything. In AKC, I will only get 4 runs but for a weekend, I'll pay about $90 on the high end. Less runs, but for me, cheaper. And the venue is closer than all the rest.
I would suggest, start in one. You said you're going to start in CPE. And after you run that for a few months, just try out another venue in your area. See how you like it. I've tried 4 venues and I like them all for different reasons. I chose to concentrate on one venue because I can't afford to play in them all. lol. If I had my choice and they weren't all so far, I'd do them all.
When you decide on a goal, then you can go forth in a specific venue. i.e. I know I will have a hard time getting the higher titles in CPE, NADAC, and USDAA due to working distance with my dog. So, I took the "easy" way out and decided to pursue a MACH in AKC. Can I do it? I think we can, but it could take awhile. So, I'm focusing on AKC (and I admit, I want that title with Koji's pedigree). But we are "playing" in other venue's too because I know Koji loves NADAC for their very spread out courses (he gets to run full out while I am huffing and puffing behind him trying to keep up).
Well, that was lengthy, lol. sorry.