Lessee,
We have battle rifles mixed in with assault rifles.
We have rifles that have been in combat mixed in with rifles that have seen no, or next to no, combat.
We have rifles that are designs that are over 50 years old in with rifles that are based on designs less than 20 years old.
And, we have no definition of what criteria are to be used or what type of conflict they'll be used in.
The question is overly simple. Even in today's high tempo conflict we see US troops using the M4 and the M14. One a compact assault rifle, the other a full size battle rifle. Each has it's applications. Each is suitable for different combat environments. Each is the "best" rifle for what it is intended for. What about the AK then? Isn't it best when used by poorly trained, poorly equipped guerrillas who can't clean it operating in dirty environments even though it lacks the accuracy of the M4? Isn't the FAL best compared to the M14 because it eats almost any crappy ammo made and still maintains reasonable accuracy?
"Best" is dependent upon what parameters have to be met.