Well if you are comparing the two then you must have one honkin' sampler in mind.. because the machinedrum is fairly pricey heheh
While the sampler may be better in terms of range of sounds you can have.. The machinedrum has its own sound, and tweakability that you can't get from samples. I'd say sequencing a relatively inexpensive sampler from it will give you the best of both worlds :)

Can't say enough great things about elektron. I own the machinedrum and the monomachine... the sounds they make are too sick, and the interface is to die for.

Cheers,
-Chris