My first point is: I'm not voting for one over the other, cause they are not even the same type of machine. So very different.
But regarding the md, I have to agree with the folks who mention that it is not just about the sounds, it is about the way it lets you make a pattern with constantly morphing, changing sound parameters. compared to the mpc, there are more parameters, and the md's interface makes it about 10 times faster to tweak a bunch of things at once. (basically everything grouped together in the same window, with 8 knobs accessible at once... you can really fly on that interface.)
Look at it this way::: on the md you have a smaller set of 'instruments' to work with, but those instruments have more range and more options. On the mpc, you can start with any sound you want, but the manipulation isn't as crazy.
I ended up getting both (1k and sps-1) and I love em both, and I use them for totally different things. If you get a md sample cd, you can learn about the sonic 'flavor', but if you want to know what the machine is all about you gotta try one, that's for sure.
When i was trying to learn what gear i liked, i bought a 1k for a week and just returned it... basically a free rental. Then I ended up buying it later once i was sure. It's a good technique
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