I've used a few types, we had a monster with a 5" or 6" cylinder for a while, it could not be stopped by knots or cross grain but it was slow unless on a newish tractor with big pump.
My favourite has been a splitfire we borrowed recently for a few cords. Its no where near as strong but its about 2-3 times faster than a normal splitter even at barely above idle. We parked it over old apple bins and split right into the bins. It could be stalled but was easy to get the piece off and you just start at an edge.
With the tractor rev'd up it could keep up to 2 or 3 guys bringing blocks to it. We have a portable conveyor we can set under it to load a truck or wagon too, makes a good team.