While I would not call it the best in L.A., a very good quality "bargain" is Stevens Steak House in the City of Commerce area:
http://www.stevenssteakhouse.com/
I've probably been there fifteen times over the last ten years. Very easy to get to (a block off the Freeway, very close to the Citadel Outlet Mall).
Massive cut of prime rib (20-22oz.) with salad, spaghetti, and veggies is $21. Service is always good, and the atmosphere is upscale Hispanic restaurant. For those not wanting steak, they have large Mexican food platters also.