daylights are prolly the 6500k lights, the more orange/yellow lights are the 2500k, btw 6500k & 2500k are just guidlines as long as they are close to this you will be alright.
I would do 18/6 unless electricity isnt an issue, from what I,ve read if your only going to use one kind of light all the way through grow and bloom the hps is better then the mh, but if you can use both then mh for veg and hps for bloom.
If you really want to maximize your yield for the size of space your useing I would definetly look into more light. what are you using for a flower light?