I'm a massive DC fanboy but even I have to concede that the GameCube version of PSO is better:

- you don't lose any unequipped items when you die (this is super annoying on the DC)

- you can level up your character to 200 instead of 100 (or 150, I forget which). Which is very useful in Ultimate campaigns (as well as lengthens the game)

- GC also comes with Episode 2, which is something like 6 extra dungeons. Some of them look absolutely gorgeous too.

The DC PSO is a fantastic game, but he Sonic Team basically doubled the scale of game when they released it on the GC.

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Edit: thinking about it, `Ultimate` mode might not even be available on the DC version. Or if it is, it's only available on the v2 of the DC version (there were two versions available for the DC). Ultimate is like another mod for Episode 1 because it comes with new skins for the mobs and the campaigns happen at different seasons and/or times of day.