I use whatever I'm using for the bass drum pedal but only when I'm pressing down. So for example, if I'm going heel up on the bass, I tend to use heel up on the hi hats as well when I clomp the hats together. This is in order to keep my balance and to keep up with the general style of music. Since heel up means louder volume and more
attack, you're probaly going to need the same for the hats. This is a generalization however. There will also be times when I'll use heel up on bass and heel down on the hi hats and vice versa. It all depends on the musical situation and honestly I don't really think about it when playing.