I think it depends on what kind of applications you want to create. What kind of information do you need to supply to the application and/or what kind of control do you need? Do you need just switches or are you adding sensors via the GPIO ports? Do you need to transfer data in via SD card or even ethernet? What are your output requirements? A few blinking LEDs or LCD/VGA output?
If you are making a blackjack card counter to put inside your shoe, the DE0-nano would be a good choice. On the other hand, the DE0 is a good choice and if you have the bucks and the student discount, the DE2 series is even more capable.