The the really really blue one. I think the packaging actually refers to 'daylight' somewhere. Mmm blue. I recently switched from 650 total watts of MH to 400 with that bulb, and don't use the 250 lamp anymore, the light is so intense I don't need it, and can put those 250 watts to work in the flower room lol.

I'd go from 4.5" to gallon pots as your next step. Read the 'continuous canopy' sticky and the 'why i should re-pot' link in it. Top of the basic section.

To determine height, just raise the light until the back of your hand held at the canopy is warm but not uncomfortably so. You can go closer if you have an air-cooled hood (GREAT invention!).