If you want to be balanced, I would either go with 18/21 or 21/18 (this last one, probably). Try to level up to 18/18, without putting any point in anything other than Athletics, Power Draw, and Weapon mastery. Then, if you think you have enough accuracy (it won't get much better anyway), go 21/18 for +14% base damage. If you need more accuracy, 18/21.
PD: I'm going with 21/18 myself, possibly 24/15, because I think at long range people can avoid your arrows very easy, and at medium range you have enough accuracy with this.