I've got a Google Nexus One and I've been seeing friends iPhone 3G and iPhone 3GS... even those that were released before the Google Nexus One look so much nicer and whatnot... I just seem to fully enjoy their interface and screen quality, as well as battery life and signal strength. I'm trying to switch from it to an iPhone 4 unlocked from Canada. So... I'd recommend iPhone 4.
iPhone4 - but then I've never used an Andriod phone (although some of my CC members swear by them ... )
I like the range of apps for the iPhone and often use mine as a mini-mobile-laptop - for example, last night (whilst shopping in Tesco's) I managed to; RDP to my office PC to check my old-style email system for confirmation my vB license had been transferred to the buyer, browse to xenForo and buy my xF license, RDP to my office PC again to download the software and FTP it onto my server, then SSH to my server in London to unzip it.
After all that I then used my Tesco Clubcard app to collect the points for my shopping ... and all from my phone. In't technology brilliant?
PS. Like many people I mostly use my i4 for games ... but don't tell anyone that ... it's just between you and me, okay?!!
PPS. The screen is amazingly crisp and clear, and I have used this one more than any mobile I've ever owned in the past.
So my brother won an Windows Phone 7 over the weekend at a Launch party in Miami, (got invited because he's one of the top phone salesmen in that area) and word has it, that the operating system for windows 7 phones maybe better than the iPhone (and the man, hugs the nuts of his beloved iPhone).
If you can wait for the windows 7 phone to give it a spin, it maybe worth your time as well. The only thing is what apps are you gonna have to have.
I am not sure of the difference in technology, however I can tell you this. The "push" feature for email on the iphone isn't a true push. Also, on blackberry, if you delete your email, it sync's the sever as well, meaning that email gets deleted from the server. Iphone has this feature but I have not gotten it to work properly.