1) 10 in Dexterity (initiative, evasion, maximum critical hit, accuracy)
2) 5 in Dexterity and 5 in Strength (maximum critical hit, greater damage)
3) Wisdom (evasion, accuracy, maximum critical hit, initiative, and experience)
In any case, it will take three hits to defeat Butarg. But I like the third option the most.
Added after 33 seconds
Oh, shoot. You can't go over the limit. Then, I guess, everything should go into Wisdom?