Boston Dim Sum
Depends on whether you want to go in town (which means Chinatown)or into the 'burbs. The Big Three in Chinatown tend to be Imperial Teahouse, Dynasty, and China Pearl. There's a few others too. Just go where the lines are. In the suburbs, two of the best are both North and serve all you can eat buffet: Far East Cafe in Woburn, and Lin Garden in Dracut.