Nyko's bulky Star Pad is a nice fit for large hands.
If you find the Gamecube controller to be too small, consider picking up Nyko's Star Pad. At first the controller may seem a little bulky but it seems suitable enough for those who complain about the default's size.
The Star Pad has a few significant changes other than its size. The start button is shaped like a star (hence the name). What sort of advantages this presents are beyond me, however the button does have a softer feel than the regular Gamecube controller. Also, the X Y B A buttons are laid out differently. The A button is much larger, while the B button is now kidney shaped. Also the buttons are set at a different angle, so some might have to get adjusted to it (but the buttons are still very easy to recognize, even subconsiously).
The analog sticks also have a different "feel" to them, so the player may have to get used to it. I also noticed that the C button would keep "twitching" every now and then, a problem that occurs if the controller is not properly adjusted to the Gamecube. Since there was nothing I could do about this, I am assuming that it only exists in the controller I received, and that others do not have this problem.
Overall, the Star Pad seems like a fairly average substitute for the regular Gamecube controller. You may want to consider it if you have large hands, but otherwise it holds no other advantages other than perhaps cost.