A classic bar, ideally including the bar itself, where you can hold your birthday, bachelor party, or other occasion. The whole space is for you and your guests - there won't be any other customers present.
Guests at a buffet eat standing up, picking up as much food and drink for themselves as they like. It may be better to have a venue without too much furniture for this, so that people can move around freely as they mingle and eat their fill.