Personally I use a Blackberry, I mostly see Blackberries used in the business environment by the middle-aged and older phones. iPhones I see being used by mainly the younger folks in their 20s.
iPhone! =D and the voice command is really working well. especially when playing music: http://www.youtube.com/watch?v=kYqNTWBPoyE
On my 3GS but increasingly jealous of the Blackberry crowd. O2 in the UK is having increasing amounts of network outages...