MWB, SAS, Spybot . . . and Windows Defender . . . are all of the same genre of ASW (antispyware). Some are very good, some so-so, none are perfect.
They have differing detection and cleaning rates, depending on the specific infection. One may only get some traces of an infection, another may only get the others. So sometimes, it is better to run two or three different programs consecutively to get all the traces.
I like SAS for real-time with NOD32 as an AV. With those and the occasional MWB scan, I don't catch anything.
There is an ASW board, of which I now forget the name, where that's ALL they talk about. Kind of like motor oil.