Wel, I suppose that depends on when you were born. If you're in the ~25-35 range, you just can't beat the nostalgia of having a NES. If you're younger, you might feel that way about the SNES.
Or, you could just get both:
I have 3 funtional (fully) NES consoles, a SNES, a SNES 2, and for some reason I bought a FC Twin