The ideal horseball horse is, for me, between 1m60 and 1m65, handy, tonic, reactive and with a little speed.
When we are looking among thoroughbreds, they naturally have that speed, so we work on their handiness with dressage work with stretching...
We need a good preparation work, with a lot of flat work so they have a good back for example.
Today, there is no perfect breed for horseball, the discipline is too young for that, so we work with thoroughbred because it is easier, and they are cheaper in particular when they are off the track thoroughbreds.
On the contrary, with Iberian horses, we have the handiness and we want them to have a better speed.