If you have the patience, I strongly suggest you hold off on both until you get the Wii because the Wii Edition is $29.99 MSRP.
If you absolutely must get it now, then I actually recommend the PS2 version not just because you get the extras the GCN version doesn't have, but also so you can be totally amazed at the graphics of the Wii version once you get it. The Wii Edition's graphics is about the same as the GCN version so you won't be as amazed if you've played that one.
Here's a comparison video. To be able to see a difference on youtube quality video really shows the gap between the PS2 and the GCN.
http://youtube.com/watch?v=5qz0LbKpZtIThe video alternates between GCN and PS2 video, starting with GCN.
The downside to the PS2 other than the graphics is the loading times. If you absolutely can't stand the PS2's 10 second loading times, then get the GCN version. Still, I suggest you hold off on both to save money.