Well, having lived here for a year, and hitting 4 spots for dim sum, I have come up with some conclusions which I wish to share.
Mandarin Kitchen: we went there today, and the food, as always, was an easy A/A+. The problem with Mandarin is the wait: it's not their fault, and it is probably a good thing that they are so busy, but if you go, you have to be willing to sacrifice about a half hour for waiting if your party is larger than 4. But those shrimp cilantro dumplings rule.
Yangtze: their food comes in at a B+ at this point. Often they are really on, but sometimes they have such a small selection it is not worth going. Some friends of mine went once and complained that they could not spend more than $30 among 5 people. The service is about a B, less busy than Mandarin, more busy than My Lee Hoa (below).
My Lee Hoa: way out in Little Canada, so the trip can be a bit much. The food, I rate it a B-, Paul says more like C+. But the service is an easy A, so fast and comfortable. Also, they have been circulating with a squid dish that looks awesome, which could push the food higher up, we just haven't gotten to order it yet.
Peking Garden: this is in Dinky Town, we have only been there once, but it seems to sit right in the middle in both food and crowds/service.