I know what you mean. I was also an iphone junky since the beginning, but I made the switch last October to a Samsung Galaxy Note 2. I'm a bit of a phone addict, and bought phones every couple of months. I hated Android for a long time, but have found that to a large extent, it has caught up and in some ways surpassed iOS.
What I hated when I moved was that there was a setting for everything! It took ages to set up to my liking. Then I had to download loads of apps again, and the free apps are often inferior on Android and riddled with annoying ads. Also, if you're a heavy media user, I find it all less seamless syncing with a computer, than iOS too. I believe HTC have now released some app to help transfer sms, contacts, notes etc to your android handset (samsung have done something similar). Other annoyances are that you may find you need to root your android handset to make backups, and also get updates in a timely manner. Everything is a bit more of a faff than iOS, but strangely, I'm happy! The eternal options make it very customisable. I don't do anything fancy, but it keeps things fresh.
I've been looking at my options for an upgrade soon and cut it down to S4, HTC One, and LG Optimus Pro. I can't see the point of the S4, the HTC looks lovely (and reviews are good), but it's limited to 32GB (a 64GB may become available later this year), and the LG hasn't got a release date. If you're not fussed by the 32GB restriction, I'd suggest the HTC would be a good first step. Don't sell your iphone though until you feel comfortable with Android though!