I've used Smog Busters the last two years, and they've always been great. I work close by, so I usually call to see how busy they are. Regardless, each check is less than 5 min, so if there's someone in front of you, they're probably almost done.
The people working there have always been very nice and friendly as well. Be sure to check their website for a printable coupon, since it usually knocks a couple bucks off (today it was $18 out-the-door). It costs $1 extra to pay with a card--if you care, then bring cash.
The results were sent to DMV instantly, and I registered online within 5 minutes of finishing the test.