My guess would be skygrid as it would fit with the server more, but personally, skyprisions sounds so fun!
I think it's kind of interesting that the top three most voted for are Skygrid, Creative & SkyPrison. Personally I'm Skygrid all the way but I think Creative & SkyPrison would be fun too!!
I would get behind a skyblock type idea with pvp and griefing on, no fly for anyone obviously. You’d create your base and they’d have one block that can’t be mined but can be blown up by creeper eggs implemented much like a lot of faction servers, people would try to protect their stuff and the only way to access someone else base would be flying there with elytra and if they have it surrounded with the unmineable block using creeped eggs for access and then looting the place. The only truly safe place items couldn’t get stolen from would be an ender chest.