I have a Samsung and I will be getting another one. If you are on this site long enough you will see a lot of questions about what is wrong with their iPhone. That and I can find things faster on my own typing, them SIRI can find it.
It depends on what you're into. If you're into simplicity then go with the iPhone. If you enjoy having alot to your device with features the iPhone doesn't have, a cool-looking overlay and tons more apps (including a different paid app for free every 24 hours), then go with the Galaxy S 4.