Pretty much all of the stone's Mark sells are at least very good stones. With good stone's, it's more about personal preference than quality stone.
Do you like hard stones, do you like soft stones, do you like......... We could list many attributes of stones, but until you've tried several, I doubt you could even answer the question.
That said, if you just buy one good set of stones (again, nothing Mark sells is junk) you probably wouldn't ever know and you'd just be happy with what you got.
If I were to buy a set of stones today, I would buy in order of acquisition:
A 1,000 grit stone - http://www.chefknivestogo.com/nubatamaume1k1.html
A 3-4,000 grit stone - http://www.chefknivestogo.com/suri50grst.html
A 500 grit stone - http://www.chefknivestogo.com/beston500.html
A 10,000 grit stone - http://www.chefknivestogo.com/na10grsust1c2.html