My personal experience was similar. I had the 3g and when I upgraded to IOS 4.0 my phone became more and more unresponsive. I felt like I was beginning to carry a brick. I was not really overly impressed with the iPhone 4 so decided to give a Droid a try. At first I liked it a lot and thought I had found the platform I liked more but as time went on there were more and more issues coming up.
For one, the battery life was not any better and in fact, it was worse. People talk about the great thing of being able to replace the battery and that sounded good at first but I did not like the idea of having to open my phone daily to replace the battery and that eventually led part of my phone to break due to excessive opening/closing. I want a phone with a battery that lasts
Then there was the operating system freezing up. At first this was just a once in awhile thing but eventually it grew to a several times day thing where I was constantly having to reset my phone. The worst time was when it happened the day my father passed away and I was trying to contact other loved ones. That was when I knew my Droid experiment was over as soon as I could upgrade.
Phone calls were atrocious and so far the phone clarity and connectivity on the i5 is outstanding.
The size and weight, while attractive to some due to being bigger and brighter and blah, blah, blah, was something that I grew to despise. I cannot believe the difference between the i5 and my HTC inspire.
Now for the good, because I don't want to be a Droid hater...the Droid was much better in integrating my gmail and in merging my gmail contacts with my facebook contacts. I am till looking for a way to do that effectively on my i5 so if anyone has suggestions I am all ears as Ross Perot said.
I loved the ability to buy from Amazon Mp3 directly on my phone and integrate that with my playlists. It appears that I will have to buy through safari link to amazon, download to my amazon cloud and then integrate into my iTunes account now. Doable but just a bit more tedious than on the Droid.
I am sure there are more positives on the Droid that I am not recalling at the moment. All in all though I find both platforms to be attractive and useful I just love the intangibles of IOS and the i5 better which is why I came back.
I hope that helps but either way you go the bottom line is that you have to choose the one that works for you because you are the one using the phone. Good luck!