The gamecube is a superior version of the main game, but the Ps2 has extra content, is pretty much what I got from it.
Gamecube:
Advantages-
Tighter and more responsive controls
Higher polycount models(looks that way, at least)
Real-time cutscenes
Dynamic Lighting
Better Particle effects
Shorter loading times
Sharper sound effects
Better environmental textures
Disadvantage -
No Separate Ways mission
No laser gun
No extra ps2 edition costumes for leon and ashley
No true widescreen support(faked widescreen)
PS2
Advantages -
Separate Ways mission
Laser gun
Additional extra costumes for Leon and Ashley that were not in the GC version
True widescreen support
Disadvantages -
Controls aren't as tight or responsive (could be controller preference)
Lower polycount models(looks that way, at least)
Pre-rendered cutscenes(costumes don't change in the cutscenes even if you're
wearing a different one)
Less lighting
Weaker Particle effects
Longer loading times
Compressed sound effects(supposedly due to lack of ram in the ps2, sound
was compressed to let it fit with all of the graphics data)
Less detailed environmental textures
Basically, the PS2 version is inferior in every way except controller(if you prefer the dual shock to the GC pad), true 16:9 support (instead of faked), and extra content (Separate Ways, additional weapon and costumes)
Edit: here is the closing comments or sum up of their article
Summing Up: If you desire greater level of options, and a more versatile experience with successive playthroughs; go with the PS2 version for all it's bonus features.
If you prefer greater level of graphical detail, more dynamic sound, and a more intense and immersive atmosphere; pick up the original GameCube version.