Stack Pack
I have had a plain mainsail cover, and Dutchman on prior boats, and currently have a Stack pack on my Beneteau 323. In general I really like the stack pack, not worrying about storing the mainsail cover and fiddling with it in a blow. Raising the sail is really easy (as long as you pay attention to the battens not getting caught) lowering it also pretty easy, though I sometimes have to go forward and give it a tug. I prefer it to the Dutchman. The only real downsides I have found on the Stack Pack are that it seems to have a bit more windage than a tight sailcover, and I find that when the sail comes down, the reefing lines drop in the cockpit, threatening to hang the unwary. Not a big deal if you tell them. I have a solid vang, but I don't know if its essential.