that's definitively a tough question...
i would probably go for the MnM because of its varied features even though it's really hard to choose between all of the Elektron's godies
you can make music with the MnM without the need of any external device... it has almost everything (apart from sampling, but hey, that belongs to the OT right?
) from SID synthesis to vocoder, effects, the bbox, a built in step sequencer, arpeggiator, MIDI sequencer! ...
if the MnM had a sampling feature, it would probably be one of the best synthesizers ever built...