I agree with the assessment that Super Mario World is a really long one unless you're going to go the cheap route by way of Star Road. Perhaps Super Mario Bros 3, no whistles? It'd still be long, and the later stages are TOUGH, but it'd be quicker than SMW.

I have both and am up for either, although I work most weekends. Still, in the rare event that I'm actually not working when you do it, I might give it a shot!