I'd have to say, I'm with IHG as my primary chain program. Mainly because I travel on my own dime and I simply find them more affordable than the other major chains and have a reasonable portfolio. Getting Platinum through the credit card doesn't hurt either, but I must admit that the benefits pretty much suck, even for Spire. On the other hand, I've gotten reasonably lucky with upgrades and the Crowne Plaza and IC properties in Asia that I've stayed at so far have been stellar. The US properties are generally severely dated, but most of my travel is now in Asia anyway, and I've been quite happy with IHG in Asia so far. I also get some decent value out of Kids eat free since I have two small kids that pretty much latch onto my legs anytime I travel anywhere and won't let go until I take them with me...
I pay for Ambassador because the BOGO certificate gives me good value.
That being said... I don't usually stay in a major global chain and tend to stay at smaller regional chains when I travel as they have generally been much better value for money. We only stay about 20-30 nights a year in hotels, and probably only 5 nights or so are actually with a major chain. Two of those would be on the BOGO certificate and another night would be the annual free night from the credit card. Lately we've been considering a trip to Phuket or Sanya so I might consider a Holiday Inn Resort.
In the end, IHG is the best one that fits my overall price range and has an acceptable level of quality at the places I've stayed. I've gotten pretty lucky with getting upgrades as well and the BOGO (From Ambassador) and annual free night (from the credit card) have been a great additional value.