If I were buying one of these phone for one of my parents, it would definitely be the blackberry, to avoid all the questions I would be bombarded with regarding how to unlock the phone, how to use apps, how to turn on the phone, etc. if either of my parents had an iPhone/android phone.
If I were buying a phone for one of my not-particularly-technologically-inclined friends, it would have to be the iPhone, for it's sheer ease, fun and utility.
If I were buying a phone for me, my brother, or one of my more tech-geeky friends, HTC Desire all the way.
But hey, I would take any of these in a flash, on account of the fact that I'm stuck with a 5-year-old Sony Ericsson brick, because my good phone got run over by a car

It really depends on what you look for in a phone. I've always been a massive tech nerd (more nerd than geek, I would say...)