A larger donkey is good to ride but they have some differences to horses.
The bigger the donkey, the more comfortable they are. Luckily American mammoths grow up to16.5 hh. They hold their heads lower so it can take a while to get used to sitting 'in the air'. Another difference is that you rock from side to side a bit more on a horse but more forward and back on a donkey.
Luckily donkeys are calmer and less 'reactive' than horses so are better for beginners. Don't worry, you can do anything with a donkey that you can do with a horse.
* Did you know that people who are allergic to horses are not allergic to donkeys
Hope this helps - Rowan (www.donkeydelights.com)