Ping Pang Pong is has some of the best dim sum in Vegas. But if you're coming for a trip from LA, I would reschedule dim sum for a weekend back at home. The food here is delicious, but the place is small and cannot accommodate everyone that tries to come. If you are determined to visit, the line moves at a snail's pace, and you can expect at least a 45 min wait on Sunday morning.
That being said, they offer the dim sum staples, and execute them well: shumai, shrimp ha gow, cha shu buns, etc. It's a great treat if you are willing to brave the painful wait times.