Best Aeon Overdrive: Delta Attack (arguably oblivion)
Strongest Aeon: Sandy
First Non-Overdrive to get 99,999: Razzia (not always)
First Overdrive to get 99,999: Oblivion
Strongest Wight Magic: Holy
Strongest Black Magic: Ultima
Strongest Healing Magic: Curagra
Strongest Life Magic: Full Life or Auto-Life
Strongest Magic: Holy
Strongest Blue (kamari) Magic: Nova (see how to get at the "overdrive" page)
Strongest Phisical Attack: Razzia
Strongest Protect Magic: Mighty Gaurd (see "overdrive" page For how to get)