There is no "best case for gaming".
It all depends on the type of/amount of components you need to fit inside, and the amount of space you have around your desk.
Mid Towers are possibly the most popular, they will fit all the standard sized components and 1 or 2 video cards. They are not that big, most of the computers you've seen in a workplace/home are mid towers.
Full Towers are for more dedicated users, they are much roomier than mid towers, and will fit EATX motherboards, and 3 or 4 video cards, water cooling gear, etc. They are also quite big and end up being pretty heavy.
You're usually best off with a mid tower.