Westin and 'W' hotels are the #2 and #1 "tier" hotels in the same company, Starwood. And it seems that the 'W' bed costs about $500 more than the "Westin" version. Fitting.
St. Regis and Luxury Collection (some of which are branded as Sheratons, strangely...) are the highest, but there isn't a strict ordering of W, Westin, Le Meridien. I'd probably say it goes W, Le Meridien, Westin, but individual properties have a lot of variation. then Sheraton, then Element and Aloft, then Four Points. There are individual Sheratons which are worse than Four Points though.
I prefer the Westin bed to the W bed; I've probably spent >100 nights in each.
http://www.westin-hotelsathome.com/bed.aspx
I was a little disappointed when I stayed in a Westin a few years ago, the bed was nice, but didn't live up to the high expectations.