The regular size Goblin is good enough .. just like Cthulhu, Silverplay, etc. For a sub-ohm atty like the Goblin, you need at the least 3ml tank capacity. I didn't consider buying the mini version because it can't take much eLiquid.
Secondly, wouldn't suggest buying the Goblins. As far as I know the negative posts are press-fit .. with a little pressure, those can come out easily. Ask Jay, he had issues with it. I sold my Goblins in a few days after using them