depends on the horse, the situation, the ride, the course, and the jump (and the upcoming jump).
If the horse is forward, or I need to make a sharp turn or have a very technical ride/jump/course I prefer automatic. If the horse is a little sticky to the jumps, hesitant, or if it's the end of a course, or where I need to add in speed, I prefer crest so I can release bigger and really encourage the horse to go.
That's just one example of which one I prefer where and why. There's a lot that goes into it - such as how my horse is approaching, how much whoa v. Go I need, and how technical the jump is, whether it's on a fox hunt, a pace, an event, a jumper round, or a hunter round, etc.