i would have to say a morgan x because of their laid back personality
A little girl at my barn has a welsh pony and he's so cute and well behaved. Another breed can be Connemara ponies, as they are great jumpers and can reach up to 15 hands so you won't outgrow them as quickly though the average is 14.2 hands. I think it's always important to look at a prospect as an individual and not only the breed of the horse.
I don’t think it really should be about the breed. every horse and pony will have their own personality. For your first horse or pony you should just look for a well trained and nurtured horse.