In my opinion, it all depends on what role you will play with your charachter. If you want to be the aggro guy who runs in first, there are arguments to be had on both strength and agility sides. More HP and power with strength, faster and therefore more swings with agility. Then again, if you are planning to be support/ambush, I would go Strength, because you are looking to get that critical strike in while your opponent is concentrating on someone else