--The regular S5 will undoubtedly be updated to 6.0. As a unique variant, the S5 Sportâ€¦is unknown. If it receives 6.0, it will likely be the last upgrade, as it shipped with 4.4.x.
--The G4 is already receiving 6.0 in some parts of the world, but the U.S. release will (as always) be slower. It is still a current flagship, so to not get the update would be quite problematic. Given LG's history of updating flagships that are a little under two years old, it is likely it will receive whatever the next major version is, too.
Processors: the S5 Sport apparently features a Snapdragon 801. The G4 features a Snapdragon 808.
--The 4 cores of the 801 are all of the same type (custom Qualcomm design), and all share the same load.
--The 6 cores of the 808 are split into 4 LITTLE and 2 big cores (LITTLE.big configuration), of an optimized (but generic ARM) design: the 4 LITTLE cores will share lower loads, and only if greater performance is needed will the load shift to the 2 big cores.
ï¼Comparing the two, I would imagine they would be similar for day-to-day tasks as well as, say, upgrading applications, playing games, etc. The 808 in the LG would have a edge due to its versatility, 64-bit capabilities, & ideal power consumption during normal tasks. The peak processing needs of applications that would use 4 or more cores might benefit more from the 801, but I imagine that to be a rare workload for a smartphone (given that desktop applications still often sit on one core).
RAM: The S5 has 2 GB of RAM. the G4 hasâ€¦3 GB? And LG is said to be less aggressive with its memory management than Samsung, so recently used applications will be able to stay in memory and resume more instantaneously. Looking at each phone, this means the LG will seem faster for day-to-day tasks, and will have room for RAM-hungry applications (games).
If you have no aversion to the LG brand, and if the price is right, and IF YOU HAVE READ REVIEWS FOR THE S5 (which will be outdated by now, so you may have to visit forums to see how the latest OS version is working for users) & THE G4 (which will be less outdated), I would go for the G4.