I gave up my iPhone for an HTC Desire, which seemed--on paper, at least--to offer more bang for the buck.
Unfortunately, the reality hasn't quiiiiite lived up to my expectations. I was constantly frustrated with AT&T when I had my iPhone, but the T-Mobile service I have now is, if you can believe it, worse. I was also looking forward to unlocking my Sensation so that I could tinker with it, but as it turns out, HTC's unlock tool isn't available to T-Mobile users, and I have yet to find a hack that works. (Even the Easy3vo unlocker won't work on my phone.)
And the Android experience hasn't lived up to the iPhone user experience, except in a few areas. The navigation is significantly better, but the user interface overall lacks the polish, and Android 2 still has some rough edges.
I had high hopes for ICS, which HTC said would be available for my sensation in January. If it's not available when my contract runs out, I'll likely go back to the iPhone.