Camco is the one they stock the most. I am not sure there is one that is better than another but if you are willing to do the work, one of the roof vent covers is a good thing to add...
Get the one that has the clips so you can remove it to work on the thing. Oh, by the way, make sure you can walk on your roof. Some won't support your weight.
These folks are saying that the vent covers have different fastening patterns..