What kind of weather is the bike going to be in and is it going to be stored under the cover. If I was storing the bike under the cover for the winter I would want the sealed plastic shelter that is available. It has a blower for air circulation and keeps the shelter erect so there is no contact with the bike.
kemo
After going thru two or three different ones...the best one is...the one you will use regularly. If it is full sized, large and bulky it has to be packed and then deployed with ease; the partial ones are small, pack easily and are deployed quickly, but not as protective. :s
You have to decide which one is right for you. I have both types, an HD full size one, when I want maximum protection...when I want quick and easy, I have a light one that fits easily in my saddlebag for daily commuting...depending on how much of a hurry, it is easy to cover and pack.
I agree with Kemo, that, if you are going to store it outside, the enclosed cover with air circulation is best, but it's expensive, then so is your bike.