I just went through the same process picking between the M8, the G3, or waiting a couple of weeks for the 2014 Moto X. I'm coming off using a blackberry for the last 5 years, but am finally getting an Android and here was what I came up with:
pros: Screen, battery promotion, camera, 3GB ram, SD card, Removable Battery, cost ($49 on Amazon/2 year)
cons: Battery Life, Overheating, LG's Skin on Android, LG updating with Android L, buttons on the back -didn't like
Pros: Battery Life, Metal construction, Sense interface, HTC supporting next 2 Android updates, Fast - no lag I've seen, cost ($49 on Amazon/2 year)
Cons: Camera is awful, no removable battery, size is tall - screen is small compared to G3
Pros: Design and construction, hands free tech, larger screen, pure Android interface,
Cons: Camera is good not great, battery is suspect, not released yet on Verizon so no real hands on. Cost ($200 ballpark when customized /2 year)
When all was said and done i picked up the M8, as the camera is good enough for me, and the other factors that I was looking for it was either at the top, or #2 on my list. It just got here today, so I'll be curious to see if I made the right choice.