Over the last few years, I have been in this order SPG Platinum, Hilton Diamond, and most recently Hyatt Diamond.
I have enjoyed suite upgrades at the W Hotels, and have several good memories of suites in New York city using Free Weekends at both W and St. Regis Club. However, SPG has watred down and diluted its benefits. They don't offer Free Weekends anymore to all members, and a number of the targetted SPG offers exclude Category 5 and 6 hotels for redemtion which is where I would want to use my nights. Also SPG does not provide benefits on Priceline/similar stays, they charge for local and 800 number calls, and they have made changes in the terms and conditions to specifically exclude specialty suites from Platinum upgrades.
Don't get me wrong, by working with the properties, I have been in the equivalent of the Presidential suite at both chains.
I like Hyatt for the generous promotions like Faster Free Nights, the Diamond amenity, and the breakfast coupons. Often at Hyatt I get a full American breakfast comp. Also they don't charge usually for 800 number calls, and they provide good customer service. I also like the 800CheckIn feature. They don't seem to be diluting and watering down their program like Hilton and SPG.
The disadvantages as stated are in the number of properties, and I do miss the W Hotels very much.