For what it's worth, my current full-time phone is an AT&T Captivate (Galaxy S). I've used a Droid X several times, and I've used prior-generation iPhones quite a few times. Never used an EVO. In my experience, the Galaxy S lags the most of all of them. I'm using LauncherPro as my home screen, and it almost always takes more than 1 second to draw the home screen when I switch to it from an app. God forbid I receive an email in K9... it takes 2-5 seconds to load K9. So yeah... I'm not terribly pleased with the Galaxy S.
I carried a Droid2 for a month - I got it and the Captivate at the same time. I installed the same apps on both of them (except for Trillian, which I can't install on the Captivate, because of AT&T's draconian policies). The Galaxy lags terribly, whereas I never got any lag - at all, ever, not even a single time - on the Droid2.
I know that the Droid2's GPU isn't spec'd comparably to the Galaxy S... what about it's other hardware? (I haven't looked it up recently... I'd memorized both of their specs immediately before buying them.) Why does (in my experience - I haven't read many comparisons between the D2 and DX or anything else) the D2 seem to fly, where everything else lags like hell? Is it really the Android 2.2 difference?