mh or hps?

i only plan to buy one set of lights - should i go with mh or hps? also, what strength? my grow space is 1.5' by 8' to the cieling - i plan to grow about a dozen plants. Advice please!

1.5feet?
that wont hold 12 plants but

a 600w could do it
HPS all day u dont want MH in flower