I know they are similar pedals (ZW-44 is made by MXR, but modeled after the SD-1 because that's what Zakk used in his rig)...but I've heard about switch problems on the ZW-44, and haven't heard many bad things about Boss pedals at all...
i'd only get an SD-1 if youre going to mod it
had one........not a bad pedal built like a tank. but to my ears it didn't sound as good as a bad monkey and no where near as versatile.
nothing wrong with my mxr zw44 i liek it better then my old sd-1, it is a bit noisy but my ns-2 takes care of that