On a side note, I find you saying that you "like customization" and your list of all apple products a contradiction.
But to be honest, you live in an apple world and all the apple products will get along with each other nicely. Which would make adding an Android item into your universe somewhat awkward.
Since you are looking at changing only one item and you appear to be a gadget person.....if you can afford to add the S3 into your mix and use it and try it exclusively for a bit would be best. Hold on to the 5 until you make a decision. Then you can sell the 5 if you prefer the S3. Or sell the S3 if you want to go back to the 5. Either phone would not lose a significant amount of value during the trial period.