There are a lot of different wall caps, roof caps, vent caps, etc. for a lot of different purposes, different duct sizes, different tastes. It's even difficult to find a consistent name for these things! Remember though, that air is lazy. It likes to take the straightest and smooth path and keep moving in the same direction as it has been moving. Tight turns and heavy back-draft dampers will slow it down.
And make sure that the air goes all the way from the inside to the outside of the house. Don't stop the path "near" the outside. Go all the way. Otherwise you may have moisture and lint and grease in places where it shouldn't be.
A good hood or termination fitting can improve the performance of an exhaust system by 55%!
