What is the best gamecube game ever

It honestly depends on the person.

My personal top 5 (In no particular order):

Timesplitters (Series)
Super Smash Bros. Melee
Mario Kart: Double Dash
Resident Evil 4
Soul Caliber 2


Some sites on the internet include the following among others:

Beyond Good and Evil
Tales of Symphonia
Eternal Darkness