Both tracks have good programs and serve pretty much the same population of racers, though for some people one track or the other is a much longer trek so you don't see them as much at the track that's a further drive.
Both have racing programs, but Encino's is better developed, since they've been doing it longer. This is the first season of regular local racing at ADT and we're still working on building a relatively self-sustaining local program that attracts both riders and spectators. The sizes of the fields at both tracks are comparable, but due to the economics of the facilities, ADT needs to have more riders, and probably more often, to keep the lights on in the long run. Given the way cycling has been going lately, and the turnout for the tour of california, it may actually be possible.
Probably the biggest difference you'll see in racing is that various pros and national teams are more likely to show up in the local races at ADT (though some pop up at Encino, too). About three weeks ago we had the Polish National Team mop the floor with us in the 1/2/3 field a couple weeks before they rode at Worlds. The various other track pro and some national teams, as well as some international riders and the occasional road pro show up occasionally, and sometimes race with the locals or do one of the structured workouts. There are also a few national team and international riders who train at ADT-- one time Jamie Staff showed up to start his workout just in time to hop into the B field at Roger's race school, allowing a friend of mine to get a view usually reserved for much higher level riders: he got to watch Jamie blow past him in a keirin.
In the masters fields its probably comparable at both tracks-- there are plenty of ex national team and national level riders in the area who still show up and race. Maybe even a little more at Encino than ADT, though some of them still race (and win) in the 1/2/3 field instead of racing masters.
Culturally they're both populated by much the same people, but run a bit differently. ADT is privately owned and operated as part of a large sports complex. Roger Young has some structured training sessions (that are very good), a race school (practice races that often include a short lecture), a bunch of open riding times, some times reserved for elite riders, and some clinics for triathletes/time trialists, as well as the usual intro classes. Encino is in a public park run by a non-profit on a slim budget. They have frequent racing, some nice classes (keirin classes, we had a madison training series, some intro to track for road racers), practice races on tuesdays, some open riding time, and the usual intro classes.
Facility-wise ADT is a *way* nicer track. It's smoother, and I love the wood banking. It also has a nice PA system and when it's raining out it's awesome to be inside at ADT with the CD player going, cruising around the track. Encino is a little ripply, and a little narrow since they raised the level of the infield, and has some other weird features. But when the weather is nice, like last weekend, it's nice to be out at Encino riding in the sun. And once the races get underway you don't think much about what's underneath your wheels anyway, you just ride it.
My recommendation would be to pick a place to live that's convenient to both tracks and your work-- there's a lot of good stuff going on at both of them, and you'll miss out if you don't go to both regularly. I've even ridden both in a single day a few times-- when traffic is ok they're about 35-40 minutes apart.
I sent you a PM with my email address-- get in touch when you get out here.