Round I) Primary canon versions only (Game Knuckles--minus Sonic Boom, due to Boom being an alternate reality from the main games and the fact that the Boom games, cartoon, and comics are all part of the same canon--vs. Earth-616 Beast)
Round II) Animated versions* (Composite).
Round III) Sonic Boom Knuckles vs. MCU Beast (X-Men films)
Bonus: IDW era Knuckles vs. Dark Beast (Earth-295/Age of Apocalypse)
*This is where things get confusing, as while the Sonic X Archie Comics series is confirmed to be a part of the Sonic X anime canon, it is ALSO considered to be a legitimate and official part of the greater Pre-Super Genesis Wave Archie Comics multiverse