For sheer stats, I would say Super. It's powered by the same power source as Super Sonic, and has fought alongside the form in canon. There is also no known evidence that Super nor the Emeralds are more generous to Sonic than anyone else, so to speak. So, Super would give Knuckles the same boost as it does for Sonic.
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u/Intelligent_Oil4005 Creator of Xeno Broly vs. Angron 15d ago
Not sure about Knuckles vs. Piccolo being debatable. Does Knuckles have anything to keep up with the Orange form?
Everything else sounds right though