...and also the number of integer factors of your base. 10 only has 1, 2, 5, and 10. Bases 8 and 6 have just as many. Bases 12 and 60 (used by the Sumerians and Babylonians) offer more convenient divisors.
Also a tradeoff with the size of the arithmetic tables one has to learn by rote. It scales with n^2. 100 entries in base 10, and just 36 in base 6, for example.