unless you plan on fishing in brutal cold weather or want to do a lot of overnight cruising where an enclosed cabin can be nice at night - go open.
With the open setup you can remove the drop curtains and be standing at your helm watching the rods and fishing. With the closed in version, if you're at the helm you'r stuck sitting by yourself while your buddies are fishing in the back, you're just driving, wondering what's so funny back there.
You just gotta ask yourself do you really plan on fishing in the dead of winter that often that you need to build a cabin to keep yourself warm?