I'll throw out my opinion based on personal experience.
Most non-UST tires will go on and stay inflated once the holes are sealed up with the sealant, just shake and rotate, easy stuff. I always run a sealant and non-UST tires for lighter weight.
I haven't noticed much of a difference mounting Racing Ralphs, Nobby Nics, Rocket Rons, and WTB's, they have all popped on and stayed put.
I'm completely sold on tubeless for the added traction, thorn protection (with sealant), and relief from snake bites. I have flatted a couple times though, nail through the tire, ripped sidewall, both would have flatted a tube. Biggest advantage for me is thorn protection, last year I must have pulled 30 thorns from my tires and never flatted, or even lost much psi.
Of course I always carry a spare tube though, just as everybody should.