This isn't the same as espresso I suppose but since it is one of the ways I brew coffee it is a subject that interests me. My conclusions so far...
All the african coffees I've tried, from Yirgacheffe to Kenyan AA, are great in the moka pot but even better in a press pot.
This is more or less true with the latin american beans I've tried too, with one exception: the Brazilian beans, both the cheaper ones and Santos. They are brilliant in the moka pot and not better in the press pot.
Now... Old Brown Java, Monsooned Malabaar and the beans I got from Sri Lanka, all three with a distinct asian flavor that is dark and earthy with very little acidity, as well as the more expensive robustas I have (don't know where from), these are all best in the moka pot IMO.