I don't know what percentage use each but both have their fans. 100 grain I guess would give you a little more speed and flatter trajectory while the 125 grain would give you a little bigger cutting area. But the increased cutting area of the 125 vs the 100 is so minor I cannot imagine there would be any noticeable difference in on game performance. More weight can help quiet a bow and aide penetration but what difference 25 grains would make with those last two would be also be minimal. Some claim that 125 grain heads are tougher but I have not seen that in my person experiences.
To me the the 25 grain difference in the two is so minor that any performance difference between the two isn't really worth mentioning.