Well, if you are concerned about battery life and you prefer stock skin over Samsung/LG toggles on notification menu etc kind of UI, I would suggest going for Xperia Z3 (provided you don't root or don't mind sacrificing some low light camera and display performance). Z3 also offers a location-based wifi (which automatically switches off data and use the wifi you have saved: I really like this function!) The multi-tasking features are also much better that LG G3, including the windowed app mode and one-hand operation tweaks
If you prefer skinned android (which I do as there are certain features that are really useful and more convenient) : Go for Note 4 instead. The display is better and battery life is better. Camera and other features are more or less on par (if not better -- HDR mode is great for taking outdoor shots) : well, UI wise I do prefer Lg's more toned down colour scheme however, Samsung's isn't that bad...just turn the screen mode to basic if you are more for accurate colours.
I really liked the customisable softkeys, the way I can choose apps to use immersive mode in my settings, knock code, the way I can double tap to turn screen off and on, the camera gestures shortcut like the fist to take a selfie, the small windowed call/sms alerts (though I switched to Textra as I want more customisability and Material look) and the 5x5 grid are the subtle software UI tweaks that make this a phone I do not regret buying. Do note that G3 has a screen that is certainly dimmer than average and a battery life that isn't as impressive as the other two (max of 5 hr SOT compared to 2+ days for Z3 on stamina mode and arnd 7hrs for Note 4).
Coming from a 2yr old S3 to a G3, this phone fantastic -- it doesn't lag, overheat and crash, or stutter everytime and badly unlike the S3. However, I find Note 4 a better buy if you plan to keep the phone for the next 2 yrs