That's my only motivation -- I want a larger screen. If the iPhone 5's screen was the size of the Samsung S3 I'd own one already and wouldn't think twice about Android. Period. (but it's not, unfortunately)
This may be your only motivation right now, but when you see what a Note 2 or S3 can do, you will realize how much more you have been missing.
It will not be an easy transition for someone that has been deeply integrated into the iOS walled garden. Please do not go into this expecting the user interface to be like iOS. It isn't and it takes some time to learn. This is like going from a Windows PC you have been using your whole life and one day getting an iMac. It looks very similar, but there are many things you have to relearn how to do.
Educating yourself ahead of time is key. Go to the stores and spend time playing with the S3 and Note 2. Learn how the settings and menu's work. Know which apps are available to replace the ones you use on iOS.
Google's cloud service is better than Apple's. Everything you do and when you do it is synced automatically (documents, photo's, apps you download, calendar events, etc. Google Now is much better than Siri, as is voice recognition.
You can very easily go into your Mac or PC, go to the folder that stores your music, photo's etc and just copy them over to your phone via drag and drop. You can do this wirelessly with Airdroid or via an SD card. Samsung's version of iTunes called Kies, sucks.
Here are some apps to look at that will likely replace what you are using on your iPhone:
Tasks (a to do list that auto syncs with Google)
Google Voice - Allows you to get a GVoice phone number and use that to make calls or text, if you wish. If you don't want to give your real phone number out, use your GVoice phone number. Also does texting and voicemail.
Google Now - Siri replacement, but better. Automatically provides you with drive times to work or home, trip schedules, meeting updates, sports scores, stock updates, etc..
aCalendar - Best calendar app you will ever use. Auto integrates and updates with Google. Much better than the stock Google calendar.
SVOX Classic - Allows you to change the phones speech output to a male or female, British, Australian and other accents.
Navspeedo - Allows you to add a speedometer to Google Maps and Navigation. This can be set to automatically turn on, adjust where you want it on screen and auto shuts off when you shut down maps or nav.
Tweetcaster Pro - Twitter client replacement
Poweramp - Best music player
Zedge - Able to download and use any notification, ringtone, announcement, wallpaper, sounds and use them on the phone. I think it has something like half a billion of these you can download and use. It is free too. And there is a PC webpage as well, so you can create a login and never lose your sounds again.
Officesuite Pro - Microsoft Office for Android. Works like a charm.
Printershare - Allows you to print to your home printer from anywhere in the world. At home you can print via wifi, usb, bluetooth, whatever. I love this app.
Beyond Pod - All your podcast needs.
Notify+ - Need to remember something and don't want to have to open and close an app to do it. Want that little note to stay in your notification center and edit it as you need to? This is the app.
Alarm by Doubletwist - Best alarm there is
TV Show Favs - Awesome app that alerts you to upcoming tv shows you watch, nice widget to give you a visual of upcoming tv shows for the week, nice led notifications, each individual show can have a different alert and provide info, and so on