Let’s go back to the original question which relates to cheap unicycles and speed.
If price is your main criterion for choice, you may end up with an unsatisfactory unicycle. “Buy cheap, buy twice.” On the other hand, it is possible to upgrade most of the components as you go along.
If speed and distance are your thing, you won’t need a splined hub, so you’ll save money there.
So, any reputable uni with square tapers will do.
You then need to consider wheel size. Undoubtedly, bigger wheels go faster, and cruise faster for longer. On this basis, the Coker will usually be the fastest in terms of top speed and cruising speed. However, larger wheels can be cumbersome and the extra time spent slowing down or speeding up for obstacles can make the average speed lower over mixed terrain.
I own a Coker and a 28. I would set out tomorrow to ride 30 miles on the Coker, or 20 miles on the 28. That’s gut feeling. I’ve done 50+ on the Coker and 30+ on the 28. I’m a reasonably experienced rider, reasonably fit, but not in the league of some of the hard cases and nutters who post here!
There are other considerations: storing and transporting a Coker can be a problem. A Coker can be risky in crowds or heavy traffic. Tyres and tubes for 28s/29s are readily available in a variety of styles and sections. Cokers have only one option.
Nothing else is a Coker, but a 28 is a good cheap versatile choice.
Put shortish cranks on a 28 and it is possible to hit over 15 mph, although you’d be doing well to average 10 mph over a journey.
An extreme option would be a 24 with silly cranks on it. With 102 mm cranks, a 24 will go like poo off a spade for short distances, and can be ridden with moderate comfort for 20 miles or more.