Join Date: Aug 2009
Location: New South Wales, Australia
I'd say some of the bigger, strong warmbloods. Often they have pretty huge paces, and can be super strong, so a beginner might have difficult riding them.
Beyond that it's hard to say. Young horses of any breed can be suited to only advanced riders. Quarter Horses, which are often well tempered, can also be fast, responsive and hot, making them unsuitable for many riders.
If you go to pony club you're almost guaranteed to see kids on Arabians, and usually some of TBs which range from quiet to hot. Same goes for Brumbies, once they're well broken they can make kids ponies, or pleasure horses.
So it's hard to say. No young or untrained horse will be suitable for someone who doesn't know what they're doing, but given the right training and temperament any breed can be suitable to a less than advanced rider.