Up until Sin, I'd say Auroch Reels are the storngest if you land it on all 3 Blitzball symbols. It does major damage to all opponents, while Attack Reels does 2/3/4/6/12 weakened (I think) attacks to random enemy targets. However, if you're playing the game 100% and max out Wakka's Strength attribute, Attack Reels comes out on top, as every hit does max damage, while Auroch Reels does 1 multi-hit attack with max damage. This means Auroch Reels is limited to 99999 damage, while Attack Reels can range from 199998 damage to 1199988, which is over a million damage!