I recently got a used Nokia 5800 and I hated touchscreen phones. However this one is quite fun and easy to use, bigger screen than on my E71. A bit chunky, but I got it cheap, all boxed and unlocked so no complains. I wouldn't compare it to an HTC Desire (well never used one) but it's even hard to compare it to a HTC Hero that my brother has. The newer touch screens are much much nicer (you don't need to press on the display, just touch it) Nokia has the older one. Android OS looks and feels a bit better but as I'm used to Nokia Symbian it was easy to use the 5800 from the start. It's a bit dated now so probably better alternatives are available. My brother found Android very easy to use whereas he hated Symbian. Not used the X6, but if I compare the 5800 to the Hero, Hero all the way if the price is not considered, easy and fun to use, loads of apps. Considering I paid 5 times more for the Hero (xmas gift for my bro) than for the 5800, I'm more than happy to use the 5800. So if You can get a similar deal on the Desire that You can get on the 5800 than go for HTC.
Also used a HTC HD with Win 6.1 and that might look ok-ish but is very complicated to use, loads of options and I think my mate who got it will soon hate it. I was helping him set up the internet and other stuff and the options menu looks like windows 95 🙂 not as easy to use as Android and too complicated compared to Symbian.