> Looks like they had 3 fingers per hand, so base 6 seems a likely choice.
Depends how they use their fingers and whether they use other body parts. There is evidence for human cultures having ranged from 4 to 10, 12, 16, and 20 (technically there are higher ones but they usually have sub-bases in that range).
You can count to 12 on a single hand (24 on two hands) by pointing phalanges with the thumb for instance. Some native cultures had base 8 using the space between the fingers rather than the fingers themselves.
Opinion: Highly composite numbers make good bases.
2, 6, 12, 60, etc
Number of fingers doesn't matter, although you can shoehorn almost any base into them. For example, base 6 lets you count to 5 on one hand and use your other to coujt multiples of 6. This lets you count to 35 on two hands.
