Been watching UFC for like 13 years, and Bellator and PFL since they started.
Only really gotten into ONE since the start of the year, and honestly, the difference in quality between ONE and all the the rest is ridiculous. ONE is just so far ahead.
Their weekly MT focused cards are better than whatever UFC are putting on these days. Even the few banger UFC PPVs usually aren't on the same level.
ONE's production value is way better too. Cool enough entrances with a ramp and a bit of spectacle and light show for every fighter, but they don't drag it all out. Meanwhile, UFC fighters just walk out from side entrance with some music you can barely hear, and no lights or anything.
UFC events often have garbage pacing. Too many finishes and they do all the boring filler segments, espeically when they have to wait for the main card slot to start for their broadcast partners. Just so much crap. Meanwhile, One just powers through a card.
Better commentators. Mitch in ONE has more energy about what he's watching than all of the UFC commentators combined. His post fight interviews blow away anything DC or Rogan do.
Lots of respect for their staff and fighters too. Loved how they gave that ref that committed suicide an awesome send off, and all the effort they put in when Victoria Lee died too.