Having both, I prefer the form factor of the Spark. And there ARE more knobs and buttons!
I've tryied machine but I don't like it, it's just a stupid thing that I can really well replicate whit simple Ableton live and drum rack.
I already have ableton so the only improvement for my drums sequence are any good machine like Tempest, TR series, Linndrum etc...Or Spark...
The hardware is so sweat but it's so difficoult to achieve the same result in the same time, so I prefer the Arturia's new solution, that Hybrid drum machine
I think that the Spark is born whit the purpose to emulate all this kind of drum machine (really well in my opinion) and help us workflow whit VSTi integration.
So for me the improvement that should be made are all others, like a real sample layering (all playing togheter), more effect's (hopefully some new and usable reverb) and an improved Host Integration (allow us to register the autonomation from all the knob not only the drum notes).