Chris, depends how much room you want the tank to take up. Do you have room for the 24 gallon, or only the 12 or 6? The possibilities are endless! I love my JBJ nanocube, and I know lots of people love their Aquapod, I don't think you can go wronge either way.
What do you want to keep in the? Knowing what you want to keep will help you decide what lighting is best for you.
Think about what you'd like, and we can all help from there.
Amanda