It all depens what you mean faster and smoother... and also what you want it for.
For brute speed the E8400 is obviously faster, higher clock, higher FSB, more cache... but it is only 2 core, so if you are using a program that can take advatage of four core the Q6600 would be better. I would also think that more and more software will come out taht will use four cores...so in a was the q6600 is more future proof.
It really depends on you, hwat you want it for and the prices.
Hope this helps