Hi
@smokarz
I'm coming from a similar situation, moving from a Galaxy S4. I considered both the G3 and newer G4. I was willing to spend the extra ~$150 for the G4 (newer, more up to date specs), but in the end I opted for a G3. In my view the G3 is pushing the upper limit of the size I want for a phone. The G4 was ever so slightly farther into "phablet" space for my comfort. I also considered Nexus 6... too big. I already have an 8" screen tablet... I want my phone to stay under 6". The ~5.5" screen of the G3 is to my eyes the perfect compromise. I was looking for something perhaps slightly larger than the S4... but not by much. The G3 fits the bill perfectly. Comparing specs G3 vs G4 didn't yield much to push me over the top. Faster processer, sure, but the G3 is faster than my S4, so I'm already getting a boost. Similar memory, screen, G4 has better spec'ed camera but not in a meaningful way...
OF course all of this is subjective, because we all have our own biases and interests.
A good way to compare the phones is to google like this:
phonearena LG G3 vs LG G4
Let us know what you decide!