Good list and nice analysis, waaalrus. Thanks for starting the new topic.
I picked up on the skatepark idea in the Ultimate wheel vs. BC wheel topic mainly because I’ve watched some skateboard and BMX videos lately just to compare them with what people are doing in unicycle videos. And the first thing I noticed was how much of the content was devoted to aerial tricks. Those are big crowd-pleasers I guess, and standard unicycles seem limited in that department. Grinds, flips, and spins, like you say.
Questions involving what’s best are tricky if everyone isn’t agreed on what constitutes “best.” I don’t think it’s necessarily what would be easiest, but then it’s hard to put a ranking on how rewarding it would be for a given person to learn the best tricks they can on a given style of unicycle. And I don’t imagine one person learning to ride all the different styles to be able to make a fair comparison between them.
I don’t think a low balance point for the sake of stability is the whole story. I personally love watching frame gliding freestyle unicylists, like Kaori Matsuzawa in Defect and many of the performers in Thomas Gossmann’s indoor videos. They’re way up there, but of course they were all on flat smooth surfaces. To me, the metric should include how impressive the trick is, but also how obvious it is that you’re doing something that no human should be able to do. 
I’d make the claim that unbikes and pegged unicycles are pretty much equivalent. You can (and people do) sit on the bars of an unbike, and unicycle seats are used as handles all the time. Clamping in a bike stem in place of unicycle seatpost is trivial, and mounting a seatpost in a bike fork wouldn’t be much harder.
Seems like a unibike (thanks, tholub) is also more or less congruent to a freewheel “penguin” unicycle.
I’ve heard of a pretty nice indoor skatepark a few miles away from me but I’ve never been. I’m so far from having even basic street skills on a standard unicycle right now that I wouldn’t waste my time or theirs by going there yet. Over the weekend, I got my 14 year old nephew to try a unicycle for the first time. He might be ready long before I am.