It depends on what you want. If you want an easy going phone and its limitations don't halt your everyday use then the iPhone series isn't a bad choice. The UI is spot on and the software alone makes it a competitive phone in the market, and it's alluring design and the iTunes & App store is what really makes it over the top. And I have to mention the customer service, hands down the best you can find anywhere other than Google itself (Google doesn't manufacture it's own mobile hardware unfortunately).
But there isn't much of case over android phones. The 4.0 and 4.1 interface and software itself is pretty inferior to iOS. Or atleast in my opinion and my experience. But the community in ROM and modding has made it so that isn't a problem. Cyanogen is a great base that is pretty much head and shoulders above iOS. It can make old android models seem like new hardware. So phone operating system, the android wins. So incredibly customizable. Something which Google aimed for and succeeded.
As hardware goes, Android wins again. The variety alone is a plus, but the new nVidia Tegra 3 and Snapdragon processors blow away Apple benchmarks in both phones and tablet-ipad tests. It's clearly better. The S III release proves to be the best phone available in the market, and the Note II which is soon to be released, but will unfortunately get shadowed by the iPhone 5 and the apple cult following. And as it's software, it's also customizable. Switchable batteries, screen, even the processor can be upgraded if you're craft enough. A friend of mine modded his S II to add on a better internal DAC for a better music output.
I currently have the Samsung Galaxy S II X. Wonderful phone, clearly better than the iPhone 4s. Glad I made such a purchase. But I will be upgrading to the Note II. Especially if the NA version gets the new Snapdragon processor that apparently shitted on Tegra 3 in benchmark tests.
It comes down to personal preference, but it's hard to argue for iPhone as compared to Android. May I ask what Android phone you had? And what iPhone you upgraded to?