imo probably the biggest differences really between the s3/4 is that the s4 is LTE as standard and thus more future proof, and on paper the batter life is bigger and the camera better, but youll still need to charge reguarly and youll probably not really notice any quality difference in photos between the two . Otherwise pretty much the same for the casual user
So much hate for iPhones...I will admit, their camera sucks and they're overpriced and Safari's not the most fantastic browser, but I have an iPad and I spend every waking moment on it. (It was a birthday present because my computer died.) It really is a fantastic piece of kit. People going 'apple products are ****e' - Apple and Samsung phones are both miracles of nature. Unbelievable.
Seriously, though, get a regular priced phone and save the rest of the money. I love my iPad but I would never have bought an iPhone. It's way too risky to keep it on you at all times - thefts, breakages...my dad just had to shell out for a new one, after the button broke and dug into some wiring. The warranty's only a year long.