Its definitely a match between SGS and Desire for me. Unless HTC spits out a 4G phone within reasonable time.
But still so hard to choose between the two. How's the UI?
Really, stuff like UI is totally irrelevant, it's both Android, both completely customizable with all sorts of apps/widgets.
You need to look purely at hardware (SGS wins, but slightly), looks (Desire, if no case), and I guess pricing if that matters. Oh, and generally new Android releases will be available for the Desire before the SGS, since the optimizing Google does for Nexus also works on Desire, but Samsung needs to do it themselves....
You have 4G over there, nationwide, or wuts? Cuz that'd be a reason to wait, can take months tho.