Realising that ISIS cranks have only ‘relatively’ recently become widely available, I wandered who currently rides cotterless/tapered cranks as their main ride and for what stye of riding.
Also, which uni and how strong have they been ?
I ride cotterless on my 36er. Haven’t had a problem yet (knock on wood) but I only ride it on road…
Isis. Most new stuff is in Isis and it is better, originally I rode cottered, what ever is on the ancient unicycles.
Isis is better in certain applications. For stuff like regular ol’ road riding or freestyle, cotterless is a perfectly good (and cheaper) alternative.
Cotterless has been around for a long time, and many have done some incredible things with cotterless cranks and hubs.
Roads in the UK are in an appalling condition and covered in pot holes.
More like aggressive muni sometiomes 
Sounds like my sidewalk! Yeah, it depends on what you are doing, but cotter less is cheaper, unless you always break it.
ISIS for better modern-day components. I also like uniformity, that way I can trade cranks between the various unis I have in my garage.
ISIS is stronger, but I’ve never had any problem with my cotterless hubs. Of course I haven’t done any 10 foot drops…
I have two unicycles with ISIS hubs. One is my Schlumpf 36", which I ride a lot. The other is my Trials, which just kind of hangs there. 
My main MUni has a Profile splined hub. My secondary MUni (29") is cotterless. My older MUni is a DM ATU (1999; first splined unicycle on the market). It has some other standard of splines.
Most of my other unicycles are cotterless; the rest have cotter pins. Cotterless is fine if you won’t be jumping around a lot, or dropping off things. If you want to do either of those things, ISIS (or otherwise splined) is recommended.