From my experience, third party memory cards on the GameCube were generally fine. Though if you're playing on the Wii, be careful of some Mad Catz branded ones. Not because they don't work, but because their geometry makes it difficult to get in and out of the Wii's memory card slots. It's been many years, so I don't remember the specific model, but I remember one of my friends had an issue where their third party memory card was jammed in the slot and couldn't be removed without an amount of force that is... unadvisable if you hope to continue using it for a long time.
Other than that, the only other thing I'd look out for with third party memory cards is probably the amount of storage space on the card. If you're
only planning on using it to play Animal Crossing, then chances are any old card will do, but if you're planning on playing multiple games, then storage limitations are going to be a thorn in your side. Animal Crossing Wiki states that one save file for Animal Crossing takes 57 blocks (plus additional blocks for the NES games and other added content), which to my recollection, isn't an insignificant number for GameCube storage. Third party memory cards run the full spectrum of either having more space than you will ever need or...
...so you'll want to research how much the model you're looking into buying has before making a purchase.
Otherwise, I think you'll be fine with just about anything.