Having used both platforms and ecosystems pretty extensively, here are my conclusions.

(I'll be comparing the iPhone 4S with HIGH-END Android devices, because that's what it competes with in terms of pricing.)

If you're a tweaker at all, you should not even consider iOS. Jailbreaking allows for some tweaks, but stability takes a hit, as well as support, updates, battery, performance, etc. The iOS jailbreak dev community is also terribly stagnant. Android, however, has an extremely active hack and dev community that is continually making old and new phones faster, capable of running the newest OS with cutting-edge features, and support them even as years pass. My Incredible from (I believe) 3 years ago still has a very strong dev community that has allowed me to put off an upgrade. It runs Ice Cream Sandwich, gets 2 full days of battery with 3G, max brightness, overclocked, and normal usage. I could get 4 out of it if I tried. That's unheard of. Incredible stuff is happening with new phones, particularly the Galaxy Nexus.

Screens. 3.5 inch screens are a thing of the past, and it's kind of a bad idea to get one now. 4.3 inches is seen as the sweet-spot, but after using a 4.65 inch screen on the GNex, I realized that bigger is better with screens. You really do have to try one.

Android phones also have better screen quality. This video hits the nail on the head, but it does not include the HTC One X, which has hands down the best screen you can get on a phone. The GNex has a relatively inferior Pentile panel, but as he says, it's an extremely good one.

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Build quality. The iPhone is built well, certainly, but it's not durable. There is a difference. It's just a fragile phone by design. I've found most Android phones to be significantly more durable and better-designed. And if you think they don't look good, think again.

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Low-end Android phones can't be compared to the iPhone, because the iPhone is a high-end device in terms of pricing. Apple simply has no low-end offerings.

4G. Android phones simply have much faster network speeds. Buying a high-end phone in 2012 without 4G is a bad idea if you're sticking with it for two years!

Many phones have removable batteries and SD card support. You can add tons of storage for so little while Apple would charge you hundreds of dollars and then max out at 64 GB. Removable batteries let you be able to use your phone for so much longer if need be, just carry and extra battery when you think you'll need it and pop it in when you do! It's also a boon for ROM flashers who often need to reset their phones more forcefully. If the phone battery loses capacity over time, like all do, you can bring it back by replacing the battery, raising the resale value or making it usable again.

I could go on, and I already got carried away. If there's anything else you want to know, just tell me.