Stuck between Galaxy S5 vs iPhone 5S

Hi everyone

I'm stuck between these two models. On one hand, I've had two Android mobile phones (Sony Ericsson Xperia X10 and Samsung Galaxy Gio), but I was really dissatisfied with their performances. Also I've worked with Galaxy S4 and I think it's way worse, laggier, and slower than iPhones. These would tilt me towards buying iPhone 5S.

But on the other hand, the new Galaxy S5 might have solved these speed issues. It also has larger screen (which I really like) and better camera.

And now I'm totally confused about which one to buy. Performance and screen size are my 1st and 2nd priorities respectively.

I'd be very thankful if you guys helped me choose the better one