The first is better than a basic forest, except it can't be fetched (and there are fetches in my cube), so it's very close to being unbalanced for a normal set. In cube I think it might actually be okay though. It only taps for one color on turn one though.
The second is perfect for aggressive decks, but hurts from turn 5 onward (on turn 4 you tap it for mana before you make your fourth land drop, though that might not be obvious to newer players, which is a strike against it).
I have to agree with anotak on the third. So that's out.
I'm inclined to go with the first one. It also promotes splashing the third color, because you are going to generate it anyway, so thats fun. I still feel there has to be something better that I haven't come up with yet.