Wait until you meet 1 and 2 star trolls. Even with the top bow they are tough.

Although at that point you got the armor and shields to melee them and trolls can be parried into a stun.

As other pointed out trolls are great for road clearing. Equip a good shield and just stand where you want the area cleared and block. The ones with a tree club work best.

Originally posted by grapplehoeker:

No, you'll lose more arrows due to less line of sight.

Actually I have lost more shots into the swarms of greydwarves trying to hit the troll behind them.