Dunno....but we still have a topic!
For me, it's either Pikachu's Thunderbolt (took out both Lance and Gary's Gyarados in LeafGreen), Manectric's Thunder (although it was so powerful it eventually hindered me by KOing Kyogre, it took out Wallace's Wailord, and Juan's Kingdra). Luxray's Discharge can also be useful in Sinnoh. Oh, my Spring2010 Pichu's Thunder was also useful, from my untouched Pichu, a STAB Thunder, 100% accurate thanks to rain, could knock the Red Gyarados down so weak it barely appeared able to fight. It actually paralyzed it too, but that was luck.