The St. Regis had a GREAT pool and a great hot tub, and was a GREAT hotel... I think you may still be able to stay there for a couple more days before it closes and goes condo. From my room in the St. Regis I could see the pool at the Westin next door in Century City. It looked really nice as well.
I don't think the westin bonaventure or the westin lax have pools. I could be wrong. And I know that the sheraton gateway lax has one, I was swimming in it yesterday. The hot tub at the sheraton lax is also not bad but we couldn't get the blowers working. I remember that the sheraton universal has a pool, but I never saw it by day. I can tell you that the management at the sheraton universal is probably the worst in all of starwood, and the chances of you getting an upgrade are almost zero.
That's all the info I can throw in.