I would go to G3... in my opinion s5 have overheating problems...
No, the S5 does not have any heating problems.
Only those phones that have a run-a-way app are experiencing heating problems.
(My S5 and my wife's S5 always feel cool to the touch regardless of what we are doing.
I have owned my S5 since release day, 14 April 2014.)
The only exception is when the battery is being charged. The biggest fix for that is to try and recharge at about 40%-50% (less time to full charge, thus less heat)
-or-
as I did, install a Qi wireless charger. The reason a Qi charger helps is the charge rate is ~730 to ~760 mA depending on model of Qi charger. I have 3 of them, just replaced a "weak Qi charger last night" with a very good one from FoneSalesman.
Back to the charge rate, at only ~750 mA charge rate, the battery is not being pushed hard enough to generate a lot of heat. That is good. It does take a bit longer, but I sleep about 10 times longer than the charger takes so who cares?
I won't repeat all the good points of the S5. I will show that the S5 can have extremely good battery life when in an idle condition. I am quite sure the LG G3 can do the same thing, but I have never owned an LG smartphone. I do have an LG flip phone, battery life on it was good, not great.
This is a typical battery discharge rate for my wife's S5. She only uses it for a telephone, nothing else.