Well I have not tried the S5, but I have had the S4 on Verizon. Given my experience with Samsung I can tell you with 100% certainty I will never buy another Samsung again. The S4 had Touchwhiz and it just isn't as fluid as stock Android. I had about 7 GB of free space left out of 16 GB. The S5 is supposedly better, but not by much.
When I switched to the Moto X (full priced from moto maker) I was and am very happy with my experience. The features on the Moto X like stock Android, active display, touchless control, and quick updates, cannot be matched by any other phone, and they way the Moto X feels in the hand is hard to explain without feeling it for yourself. But it feels great.
It's all a matter of opinion, but if I had to choose between the Moto X and the S5 I would go with the Moto X. It's not as specked out, but the overall experience will be better. The screen is just as good as a 1080p screen, and stock Android is miles better than any OEM skin.
If I were you I would save the money and go with the Moto X. However, eBay phones can sometimes be sketchy, so if you go that route be careful. The better route would be to get one through Moto Maker. You can customize your phone to your liking, you get the full year of warrantee and Motorola is very willing to give replacements. They will even let you keep the current phone while you wait for the replacement. But that's only with Moto Maker. They are going for $400 for the 16gb model as of now. If you have a ".edu" email address you can pick up the Moto X for $360. Best of all shipping is free on all Moto X orders.
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