Pay extra for the UW version.
Like the title says. The UW expands the Machinedrum so it can use samples, sample itself, etc... Allows the machinedrum to reach its true potential.
The SPS-1 is also fine on its own as well. I would just highly recommend paying extra for the UW feature set.
What else can I say about this drum machine that hasn't already been said? It is fantastic! It hits hard! It literally makes millions of sounds! The sequencer is bananas! It is durable! Instant dance/IDM/trance/Dubstep/hip hop/dub/etc! It makes lesser drum machines flee for their lives!
Also, by far the EASIEST electron device to use. Works equally well in a live or studio environment.