I'm thinking of buying a diamond stone for lapping. I have three Naniwa SS stones (1, 3, 8) and three welsh slate stones (DT, Yellow Lake and the Purple stone) and due to the shipping cost on the DMT stone it will cost around $85, meaning that I can get an ATOMA stone for only $5 more.

Which is generally thought to be better for lapping? And which ATOMA stone would be best (140, 400, 600 or 1200) for lapping these stones?