I don't know what the "best" option is - Tenthirty, Azeotrope, and myself are all using the 315w CDMs w/ electronic ballasts, and are all very impressed with the results so far. As far as I know, only Azeo has used the other CMH variants, and he used them for several years before changing over. The only downside to the 315s that I've seen are the cost of the components and their availability, but both seem to be improving.