I'll keep this brief.
Two weeks ago I got the iPhone 6, and six months ago I got the S5. Here are my quick impressions on some key areas.
Screen:
The iPhone 6 screen is way more usable outdoors, and looks about as sharp as the S5 despite the iPhone having lower resolution and PPI. The auto brightness feature works better on iPhone 6.
In terms of contrast and blacks, the S5 wins because of AMOLED but it's not as dramatic as you'd think. For LCD iPhone 6 blacks are better than S5 whites. The iPhone is on the coolish side, but there is an evident blueish haze on S5 whites.
The bigger S5 screen does games and video more justice, and the larger screen + higher resolution means more content on the screen at any given time.
Sound:
The S5 DAC does better with headphones of all makes, even Apple's. The universal and adjustable EQ helps. Since I am using headphones all the time in the gym, when running, and biking, this is important.
The iPhone has a better speaker. Louder, punchier, clearer.
Build and feel:
LOL not even close. The iPhone 6 feels and looks like the better product.
UI Experience:
iOS 8 just flows smoother, nicer and in a more appealing away. This does not men S5 Touchwiz is slow or lag.s It just feels less refined and chunkier.
iOS 8 has better lock screen notifications.
iOS is not all that simple. Enabling extensions and app to app access is not all that intuitive, where android has this all baked in, so it's just easier.
Camera:
The iPhone 6 camera is better. Clarity, details, color accuracy, shutter speed, interface simplicity.
However the difference is not HUGE expect when we are talking lowlight, where the iPhone does a better job overall.
Battery life:
S5 wins by an hour on average during my average daily use, iPhone is a 10 hour life, and S5 is an 11-12 hour phone not counting ultra power save.
Lifestyle product:
The more iPhone's compact body, Siri, iCloud, Touch ID, full headphone aftermarket support, health tracking apps and ecosystem with my Mac and wife's iPhone 5 just makes it a better lifestyle product for me.
There can be only one...
The iPhone 6 was returned and the S5 stayed.
Why?
iOS 8 is half baked. Limited widget and extensions means the iPhone 6 is hamstrung out the box.
Apple Pay is not functional yet.
No iWatch.
Handoff is still a bit dodgy.
iCloud drive's interface still doesn't make as much sense as Dropbox.
Swiftkey and keyboards don't work right.
In the end there isn't a huge enough reason for me to change in terms of what I do day in and day out. Not enough for me to incur the additional AT&T monthly NEXT costs at least.
So yes, I think the iPhone 6 is the better all around product, but RIGHT NOW, going with the iPhone 6 is a downgrade because iOS 8 is half baked and poorly supported by Devs.
I wasn't too happy about losing dual apps on the screen either. That's a lot of extra iPhone screen with not many new ways to use it. I felt blind on the iPhone because all the widgets I normally use on android aren't on iOS yet and actually opening App's to see my feeds was slow and tedious.
I'll be revisiting the iPhone 6 once the Apple Watch drops. Thats a few months from now so hopefully by then devs will have it together and kinks will be ironed out.
For now I will stick with my Samsung S5.