A&W's dim sum is pretty good, but not on the level of the good San Gabriel Valley dim sum houses. (I would say A&W is pretty comparable to Empress Pavilion in recent years.) While the drive to San Gabriel is probably as quick from North Hollywood/Studio City in no traffic, A&W serves dim sum every day.
A&W is on the corner of Reseda and Prarie (just north of Nordhoff and not too far from the 118.)
A&W Seafood on Reseda Blvd. in Northridge has dim sum on carts, but for the time it takes to drive up to Northridge, you could drive downtown where the product at Ocean is better and more varied than A&W. Even the SGV doesn't take that long to get to on weekend mornings. We can be in San Gabriel in less than 1/2 hour from Sherman Oaks.