I prefer 18/6.... it's suggested (not proven to my knowledge) that you get better root growth during dark periods. In addition to that it's not such a shock to the plant when you change from 18/6 to 12/12 as opposed to going from 24/0 to 12/12.

That's my opinion anyway; but either way.. 24/0 and 18/6 are both prove to work. Whichever you use is your own personal preference.

I choose 18/6 just because I'm a cheap ass and I like to save electricity. :thumbsup: