Well there's a home button and there's the whole symmetry aspect, and you can't deny that Touch ID works really well, so apple is gonna be keeping that home button for a while until they find something that works just as well or better.
Sony and HTC both have software buttons, there's no excuse.
I think I read somewhere that HTC was claiming the bezels allow for more internal stuff (probably related to the speakers and battery). I'd bet Sony would say the same, especially considering the relatively huge battery in the Z3. I don't like big bezels either, but both phones have pretty damn good battery life along with sizable screens, so I'd say the space isn't exactly going to waste. Meanwhile, the battery life on the 6 (specifically the 6, not the 6 plus) is the same or marginally better than the 5S, which isn't really worth bragging about.
I know, I know, Touch ID and symmetry, but at the end of the day, iPhones have pretty massive bezels, which make them feel much larger than their screen sizes suggest
Anyway it honestly sounds like you've already convinced yourself you want a 6 or 6 plus and are just working backwards from there. Which is fine. And I'm saying that as someone whose current daily driver is a 5S, who's looking to replace it and is comfortable with iOS or Android. I've been disappointed with damn near every flagship phone this year for some reason or another
HTC One M8 - Lackluster backside camera
Galaxy S5 - Not a fan of TouchWiz and flagship price for a phone that doesn't feel or look like it
LG G3 - Battery life and performance issues; not a big fan of their skin either
Xperia Z3 - Only available on T-Mobile or full price unlocked
Note 4 - TouchWiz and worrying about updates
Nexus 6 - Too big for my tastes
iPhone 6 - Battery life not significantly better than the 5S
iPhone 6 Plus - Big bezels make the phone feel more unwieldy than its screen size suggests
To be fair, I'd probably say 2014 has too many good choices, but none that are far and away the winner, which makes choosing one that much harder. But I'm leaning towards either the Note 4 or the iPhone 6 or 6 Plus personally