Lots of people seem to be happy switching to Starwood. The Westin properties I've visited have all been top notch and I've been tempted to jump based on similar reasons as you.

IMO, Hilton is not much better, and the properties are worse. Overseas there seems to be more Hilton properties but stateside I'm using Marriott 95% of the time.

If you jump ship, please write a nice letter to Marriott management letting them know why you did.