It can be either. It's up to the contestant what size cupcake they make. Some cupcake businesses offer only minis, and sometimes bakers who normally sell full-size cupcakes decide to bake minis.
Most of the time on the show, they're full-size cupcakes. I kind of wish they had a rule against minis...it definitely seems like a bit less 'work' for the final round. But minis are harder to decorate impressively!