I have had all three, and they all have their high points. I am currently carrying the G3 and the s5, I sent the HTC one back two weeks ago.
IMO, out of these three fine devices, the G3 gets my nod as probably the best phone available right now (and the Note 3).
The build quality is great, the screen is FANTASTIC, and once you get used to the button placement, you wonder why it took a while for someone to try it like that.
The s5 is great as well. Slightly smaller than the g3, and the one. It is water resistant, and has the most features.
The HTC One is hands down the best looking of not only these three (g3 is a close second), but of any device available in my opinion.
That aluminum body is heavy however, and its almost as big as the g3 while giving up some screen size.