First I want to say that E7 Can't be compared to the N900 because of it'sraw power like hawaii said. It won't have features like multi boot to maemo etc.... And I don't like the keyboard.

N8 however is so slow. It lags at the homescreen when you switch between desktop. Out of the 3 (N8, C7, and E7) I think C7 is the fastest.

Your question is just a matter of symbian^³ or android. Just go with what would fit your needs and where you're going to be contended.

After all this and you still can't decides. Just a buy nokia 3210