I think you should just keep the S5, regardless of what device you purchase, it will be out of date in about 6 days...
But, that "out of date" is really a matter of semantics because none of us will ever really agree on what is "more important" to "make better".
And consider that at the current technology level, it is getting extremely hard to make Significant Improvements in performance.
We have a hand full now of Flagship products to choose from, and none of them are "bad". They are just "different" in small ways of approaching the same problems/issues.
A digital camera will never be as good as a film camera when it comes to low light. As far as critical performance in daylight goes, digital cameras are getting very close to the same level of performance as most film cameras.
But for me, and I suspect for 99.995% of the folks "out there", the ability to snap 1,000 pictures and then delete all but the 50 best shots far outweighs any technical drawbacks of a digital camera versus a film camera. I can't afford film anyway, that is why I quit using my Nikon over a decade ago... it cost more to process and print the pictures than the film cost in the first place.
The difference in the Radio tx/rx capabilities is also extremely close. There is more difference between models of the same brand than there are between equivalent models of different brands when it comes to "loosing the signal" and dropping out a call.
The proposed S6 might be a geewhiz device, but nothing on it will vastly be an improvement over the S5.
Stay with your S5 and enjoy it... I just yesterday took my wife's S4 mini in and traded it up for another S5 to be added to our household.
I had ordered her the S4 mini because I could get it for $0.99 (yes, 99 cents) and let her try it for 14 days and find out if she would be able to transition over from her old flip phone. Well, she stumbled a lot, but she likes it pretty good. Especially being able to receive pictures from the kids.
Downside? not much, I got her the S5 for $98.01 upgrade from the S4 mini... Verizon treats their archived customers right.... been with them for 20 years now.
. oh, the differences between makes can just about be compensated for by choosing an appropriate application to give that feature to any new device.