You really cannot compare these two devices…
The MPC can do a lot of things the octatrack cannot do, and vice versa.
I’d say, if you are more into “open composing”, you will feel that the MPC is more useful.
If you like working in a defined space, and in there having a lot of choices, the Octatrack is yours.
Why is that?
MPC: As many tracks as you want for trying out stuff. a pattern can have as many bars you like. Traditional sampler approach, powered by a classic Midi Sequencer.
Octatrack: 8 Tracks. 4 Bar Loops, and not to forget the weird 4 Parts System. That’s it. But within these confines, you can unleash a lot of creative stuff with p-locked effects, scenes, micro timing, Part switching, etc…
Everytime I try to work on the Octatrack as I would with the MPC (which I had for almost 14 years now, so it’s kind of second nature to me) I start to get frustrated.
So, don’t make the mistake and try to compare these two.