If you want the best overall service, enjoy the ocean, and want a laid back vacation: Laguna Niguel hands-down.
With respect to the Sandpiper, if you have any kind of class and/or are over 35 years old, I would not go there. The dirty bird is responsible for weekly bar fights, DUIs, and drunk sluts who puke all over the street. Unless you find that kind of thing fun...
RC LA is shiny and new, but I find the actual city of LA boring (and I live here!). The excitement of LA Live wears off within the first 24 hours. Then you'll find yourself driving 30-60 minutes to do anything fun.