If you are a beginner, and are wondering which type of unicycle to buy, the choices are limited. Many of the specialized unicycles mentioned in Types of Unicycles are not suitable for a beginner, because they are harder to learn to ride. Selecting the proper type of unicycle will make the learning process much easier. Once you are riding, you can move on to a more specialized unicycle tailored for the type of riding you like to do.
A 20” to 24” wheel is easiest to control, and the longer cranks are easier to use while you are learning. Thus, the ideal starter unicycle for a child or an adult is one with a crank length of at least 114mm minimum on a 20″ wheel or at least 125mm on a 24” wheel. Children younger than 7 years old may need to start on a smaller 16” wheel.
It is also important to have the seat at the right height. For most riding, the seat height (measured at the lowest dip of the saddle) should be an inch or two below your navel. If your seat post is too long, it can be shortened by using a pipe cutter or hacksaw. If your seat post is too short, you can purchase a longer seat post at one of the online unicycle stores for about ten dollars.
The only other choice you must make is whether to buy a fat-tire unicycle (trials or smaller muni) or a smooth-tire freestyle unicycle. A freestyle unicycle is suitable for gym riding or outdoor riding on pavement or smooth trails. A trials unicycle, with its fatter tire, is suitable for jumping curbs and other obstacles, and for riding on rougher trails. The choice is up to you.
Once you buy your first unicycle, it is time to learn to ride it. See Learning to Ride for some instructions on getting started.