Had an iPhone, now have an HTC desire.
In terms of which is better then I suppose it comes down to what you might use it for.
IPhone wins
Music player
Email
Apps – at the moment the quantity and possibly the quality of iPhone apps are better than Android market, but as the Android market grows I'm sure it'll be on a par with Apple pretty soon.
Voice control – always worked really well for me.
Desire wins
Speed
Camera – really impressive camera. Lots of adjustment and a flash
Multitasking
Can use memory as flash drive
Memory is expandable
Can get a separate battery
Like the haptic feedback too.
I can read singletrack mag on it too.
I'm really impressed with the desire. I originally upgraded with the idea of getting rid of the desire, but after using it for a day I had my doubts after a couple of weeks I decided to keep the desire.
Only thing I really miss is the music player of the iPhone.