What is the best type of convention?

Geek/fandom cons which is a conventions that tries to include every fandom

Single theme cons which have a certain theme, like anime, video games, comics, etc.

Single fandom cons which are conventions centered around a single fandom, such as Doctover Who, Furry, Pokemon, etc.

I think fandom cons are usually a mess, they have no clue what they going for. Single fandom cons are just boring, especially 3 day ones.