Why do we write $a^n$ instead of $^n\!a$ for exponentiation? What benefit is there to writing the base before the exponent? With addition and multiplication order doesn't matter since $a + b = b + a$, so why was $a^n$ chosen, and who popularised this notation?
To me the first is preferable since it's a logical choice, as you put the number in front when you add: $$a+a+a = 3a$$ Thus it makes sense to write: $$a\times a\times a = \,^3\!a$$
It would also retain left-associativity as is commonly used with subtraction and division: $$(a\text{^} b)\text{^}c = \,^\left(^ab\right)c$$
Historically the best choice isn't always the one which got popularised, but there must have been some reason why this choice were made and preferred in its period of invention.
A similar question was previously asked on Mathematics.