Free originates from the Arcade scene, where people had to put quarters in the machine to play. Someone that put a quarter to play against you, and sucked was essentially a free turn.

So, when it comes to first person shooters “Best” typically comes down to who has the higher TTK, and survivavility rate. As a rule of thumb, hitscan weapons do the most damage on an accurate player since their weapons will always be glued to an opponents body of mass or head.