The choices are many and varied, with 7 levels to have a go at, each level named after a colour of the rainbow! The combinations are, in summary: walking with two reins; walking with one rein; walk and trot with two reins; walk and trot with one rein; walk, trot and canter with two reins; walk, trot and canter with one rein; and, finally, the elite walk, trot and canter bridleless (no reins).
For more detail about each level, see the Horse Agility Club website.