I've used Masterpark Garage about 3 times in the last two months. Each time, I was picked up within 5 minutes. I did notice that they do have a fairly hefty surcharge. I've been giving them a try because of the various free parking coupons they have been giving out. I will go back to my standard place once the free parking coupons dry up.

I typically use Airstar/Shuttlepark. I usually have to wait 10 minutes or more for them. While I hate the wait, they do have good rates (about $8.50/day) plus a great frequent parking program. I usually end up earning a free day of parking after every third trip. Most of my trips are short 2 days/1 night. Shuttlepark2 is also part of the same frequent parking club. It's all automatic and tied to a designated credit card. You can see your point total online.