My only experience with unicycles is having started on a 20" and rode that for a few months and then moved to a 24" MUni, which I have ridden for most of the last year. I have never ridden a stock 24". The 20" is great for freestyle and nut much good for getting around, IMHO, the wheel is just too small for my needs in that respect.
The 24" MUni is great for off road and climbing with its 170mm cranks. It is really slow for going around the neighborhood, though I do take it for spins at night for light urban trials.
Having now ridden the 28" uni, it seems like it’s a great all-around comprimise between the above mentioned unis.
The narrow tire, higher psi, and the increased diameter give you a decent vehicle to get around town, say a mile or two, maybe three. The increased speed isn’t breath taking, but it is faster than the MUni with the long cranks. I had it built with a really tough wheel, so I can ride it off curbs and up as well and I can hop on it without worrying about tacoing the wheel. This makes it just that much more fun to ride. I haven’t taken it up any hills nearby, but I was told it climbs quite well due to the decreased wheel mass when compared to a 24" with GAZZ. I may eventually add a nobby tire to it.
The 28’er is surprisingly nimble and with the 700 x 35C tire it is also a soft ride.
I would like to go a little lower on the cranks on the 28". Currently I have 150’s on them, but would like to try 140’s.
Keep in mind, that my time on the 28" is really limited. At this point, a little less than 1 hour.
I have never ridden a Coker, mainly due to fear of going really fast on a Unicycle and finances. But, it seems that the Coker would really let you cover some ground as so many prefer on this trusty steed.
One last point. I really noticed that my hips want to pull to the right when I ride the 28". I have tried many things to eliminate this. The advice that I have received is just to ride on it until my body adjusts to the new and different setup. That’s what I am doing now. If you get a 28" or any other new unicycle, this may happen to you. It’s just supposed to be part of New Unicycle Syndrom or NUS.