Excellent question. I think it really depends upon what you want to do, and what you like. I am admittedly biased toward NASA because we're a much more flexible and progressive organization IMHO, but here goes:

For autocross, NASA events cost more money but offer more runs.

For rallycross or road rally, SCCA has great programs (NASA doesn't have any programs - we just did our first rallycross this past weekend and aren't sure if we'll ever do another one.)

For track schools, NASA has cornered the market with the HPDE program. (Our last one of the year is this weekend at Summit Point, actually... but we've got a single-day at VIR in November and we'll be at VIR-Full for 3 days in February.) SCCA doesn't offer a similar nearby program where a driver can get in-car instruction on a roadcourse for several hours per weekend.

For Time Trials, NASA does "CircuitCross" Time-Attack style autocrosses on smaller road courses (VIR-Patriot in particular) and open-passing timed sessions on roadcourses during the HPDE weekends, for the experienced drivers. SCCA doesn't do those things as far as I know (although their Solo I program is kinda close.)

With NASA, you can use a street car for any of the things mentioned above.

For roadracing, it's hard to compare to the DC Region SCCA's excellent MARRS series. They've been around forever and set the standard by which everyone else is compared. They unfortunately don't offer quite as much seat time in a weekend as NASA roadracing does, though. And they don't officially recognize the single best/cheapest roadracing class available right now IMHO (NASA Spec E30 for '87-'91 BMW 325i's.) But for something like a Spec Miata or Spec RX-7 or anything openwheel... SCCA's the best. Huge entry lists, tons of great competition & close racing, etc.

For working & becoming an official, SCCA volunteers usually get nothing (but *maybe* expenses if they've been doing it for enough years.)

NASA volunteers can get free hotels, free meals, and best of all... worker credits toward later events (work 2 roadcourse weekends as a flagger, timer, tech inspector, etc and drive one HPDE weekend for free as a result, etc.)

Also, money-wise, NASA yearly membership is cheaper than SCCA and you get a subscription to _Grassroots Motorsports_ magazine among other things.

Long story short, I'd recommend going to SCCA and NASA events and deciding for yourself. IMHO, all that really matters is that you're a part of one or the other or both, otherwise you'll be missing a whole lot of fun with cars.

Hope it helps,

Jon