I've seen a Samsung Captivate (the AT&T version of the Galaxy S) and it is a pretty sweet phone. But I just bought a Droid X, the GPS issues the Galaxy S has been having is a dealbreaker for me. I use my GPS quite often. So instead of waiting for the Verizon version of the Galaxy S to come out and then waiting for the GPS fix, I went with something else without a known glaring issue. It's like the iPhone4 antenna problem in my mind; both issues must have been known before the phone was released, but it was released anyways, and neither problem is fixed yet by the manufacturer. There are 3rd party GPS fixes for the Samsung, and the bumpers/cases mask the antenna problems on the Apple, but the root issue is still there and unresolved in both cases. And Samsung has a reputation for not supporting stuff after it's released. I had a Samsung TV that had a main board issue less than 2 years after I bought it, and a repairman couldn't even source a new part from Samsung, they didn't carry it or even support that TV anymore. And the previous Samsung phone I had had the screen die right at the 2 year mark.
Anyways, to paraphrase, as nice as the Galaxy S is, and as much as I want to love it, Samsung has left a little bit of a sour taste in my mouth, so I'd suggest you go with the HTC Desire.