Whether you are a happy hacker or hacking an elite event horse its really important to work the horse evenly on both diagonals and leg leads rather than letting the horse favour one lead as over time this will create weaknesses that can lead to injuries and stiffness.
For example, if I was out cantering on the hills, I would alternate my legs leads from hill to hill. If I was trotting I’d ride one hill on one diagonal and the next on the opposite.
If a horse is weaker on one diagonal I would perhaps ride two to one so that they can strengthen up. As soon as you feel your horse is even on both diagonals, stop doing this.