One thing to keep in mind is teh GS5 is going to be available in more markets than the Z2. I'm not sure if you're in the US, but the only news for the Z2 is a rumor it may come to Verizon.
Interesting. I thought that Sony was committed to only releasing their high end products on GSM carriers, at least outside of Japan. To the OP, the Z2 is probably a better all around piece of equipment out of the box. Two things, tho. First, in my experience, Sony mobile products degrade quickly, both the hardware (case, battery, screen) and the software (I can't explain it but we all know how even a reset phone starts to drag after a while). Second, since the Z1 never got a proper release in the US, it's basically vaporware relative to the S5, which you can have in your hand in a little over a week.