This is a regular lunch spot for me and my co-workers. If you go in at lunch time, you will see that it is a regular place for a lot of people. It can get very busy, but the staff does a great job of providing top notch service even when packed.
I am not an expert on Thai food, but I have not tried anything there that wasn't outstanding. It is really hard to come up with a favorite, just try any of the lunch specials and you can't go wrong.
One word of warning, they let you pick your level of spiciness, and I find that if you are sensitive to spicy food, you might want to be a bit conservative.