1) WiFi (well duh)
2) You can take it wherever you go, and play it for short periods of time on the go (which is kind of perfect for animal crossing)
3) It's a lot easier to get rich.
However there is the disadvantage; you can probably get the GC version second hand now a lot cheaper than the DS verson. Also the wii will almost certainly have one, so if your not in any huge rush, you may like to wait for that. It'll have wifi and there is a roumer that you will use the wiimote to do animal crossing actions (dig holes, chop down trees, plant flowers, drag sofas across your room etc)