I had the same question yesterday, especially since the strategy guide suggests 18, 15, 11, 8, 16, 7 (for both: two-handed and two weapon style).
As it turned out everybody but the strategy guide seems to stress the importance of dexterity. So I ended up with (Aumau) 18, 10, 18, 8, 17, 7 and switching between both styles at which two weapons seemed much better working - mainly when he is soloing.
I really did not (do not) understand how exactly attack speed actually works, but testing a barbarian with 18,15, 11, 8, 16, 7 against one with high dexterity (18) was a clear cut case: with high dex you will be much more successful (in the two first playing hours) whereas a barb with low dex is a helpless thing to watch (after Frenzy runs out). Maybe it all will change later in the game, but low-dex (11) barb felt odd (and couldn't solo the early groups [on hard]). So I went with what the forum told in the first place.
What I still want to know: how important are perception and resolve offense-wise?