Ha, I have three of those in my possession right now! I just went though this decision process so hopefully some of my thoughts will help you narrow down what's important for YOU as well.
Have had the 928 for a bit over a year. Unlimited data customer, on a family plan. Had an upgrade available on my line, and saw the news about Verizon tightening the screws on one of the upgrade loophole's. So I started considering my options.
I did consider an iPhone, had been thinking of switching platforms anyway. I'm not really in love with where 8.1 is headed, however, you are so limited in hardware. What Apple gives, is what you get. So likely no wireless charging, definitely no dedicated camera button, likely no NFC, but probably best combination of MS/Google/Apple support.
I bought an LG G3 mostly with the intention to sell, but also since I was curious to see what a modern top flight Android device could offer.
Spec wise, obviously the G3 offers just about everything, and with a replacement back (hey Verizon, thanks for removing it in the first place) you can have Qi charging working again. 13 mp OIS camera, laser focusing, sounds nice. In usage, the default camera app has basically NO control. Touch screen, photo is taken. I tried finding something free to control shutter speed, but didn't really find anything full featured and free (like one app would take a long exposure, but without paying $3 or $4 all I got was low resolution captures). It seems to be really aggressive with the compression on it's pictures, and low light (dim lamps) it is very noisy.
It is a big honkin phone too. Some things might be one hand, but it is definitely in two hand territory quite often. On the bright side, it has double tap to wake and sleep. Woot.
My wife's sister also had an upgrade available, so she bought an Icon for free ($30 upgrade fee), and then swapped her flip phone back onto the line. I got Verizon to lower her monthly bill by $20+/mo as well, so didn't feel bad about her giving me an Icon for the cost of the upgrade fee.
I'm using the Icon right now, and it has some good and bad.
Screen is nice. Brighter and whiter than my 928, shows more. Comparable to the jump from the smaller phones to the 928 was. Glance will never come to it, but double tap to wake is expected with the 8.1/Cyan update. Speaker is inferior to the 928 by far. Single slot in the back, similar to the 520, easy to block, but also just quieter. Faster loading apps for sure, but overall very hard to see much performance difference between it and the 928. Qi charging built in, camera button. Comes with an old version of Nokia Pro Camera, I like it versus the new revisions lol.
Negatives, not a lot of shiny new features, which is where we get to the M8. The lure of stereo front speakers, IR remote control, functioning tap to wake, are all pluses.
So:
LG G3
Hardware is beautiful
Screen is gorgeous
Memory card slot
Camera has all the right tools, seems like software is holding it back though
Very large phone though
Costs extra for Qi charging
You could actually use it to buy things at the store
Icon
You pretty much know what you are getting
it's the 928+1
Qi charging, dedicated camera button
20 megapixels, takes more work in extreme low light than the 928 though
Better software for photo control
No memory card
I don't have the M8, but:
nice looking!
what's with the logo strip with no buttons (it offends me!)
Pimpin speakers
they got pimped by the camera salesman though
And again this year when they lost OIS lol
IR REMOTE
But, no Qi, no dedicated camera button.
But has memory card slot.
(G3 has IR Remote as well. Holy hell. Would be so great to turn on the TV, adjust volume, control Roku...)
Sorry for rambling post, tired and can barely keep my eyes open. Still pondering if I will clothe my Icon. Or just buy a warranty for it heh.