I decided to switch to the galaxy s4 from my iphone 4s, and while they are both great phones, I had to go back to the iphone even though on paper it is inferior.
The straw that broke the camels back was the instability of the AT&T messaging application that you had to use on the S4 to view visual voicemails. The problem was that application also managed MMS services as well, and to have that application be unstable was really frustrating.
The main issue is that the software on the iPhone has a tighter integration with the operating system, other software and the hardware. The galaxy S4 phone seems to have a ton of features stuffed into a hard to HANDle package.