I have a QH. Pretty much the opposite from Supermane though; he's rather lazy, especially at the canter. However I'm assuming you know this horse you're wanting to lease, so I'm not exactly 100% sure what you're asking...
It really depends on the horse. Mine isn't high-strung or afraid of anything really. I tried free-lounging him with a lounge whip once and he stood there and looked at me like "uh wth R you DOIN with that thing mom?"
I've pretty much known QH's to be very calm and sensible. They can get a tad stubborn so I hear, but mine is pretty good.
SORRY I RAMBLED SO MUCH. I just realized how all-over this post must be.