Yusuke, easily.
On sheer terms of strength, speed, the output of his attacks, and durability, Yusuke outdoes Luke in every single area. All it takes is him landing one hit and Luke's relatively frail human body is irreversibly ****ed, and Yusuke's done way more than one hit on people a lot faster and stronger.
Luke's "strong" and all, but he's a glass cannon and all it takes is someone to be even slightly able to deal with his level of speed (ie: sub-early DBZ) or output (lightsaber's good, but the level of Yusuke's stuff later on is getting towards respectable DBZ level, and even Kuwabara's flame sword damn near matches the lightsaber and he's practically a jobber relative to everyone else).
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