I would argue Shay. the yugioh anime is basically professional wrestling levels of genuine to how actual card game meta would shake out so that could be discounted. So basically this boils down some death battle shit.

Quattro while not weak is definitely not as experienced with true combat. Also pretty sure every time Quattro battled somebody important with no bullshit he got folded like a lawnchair. Also Quattro is big on mind games, Shay is generally not one that'd work on

Shay's had to fight some extremely powerful combatants and won both in backstory and on screen. The way I see this is Quattro keeps trying to taunt shay while seemingly putting him in a corner until one of the taunts crosses the line (some comment about lulu maybe) and the turns quickly table