So which type of light would be the best for my grow description? MH for veg? HPS for flowering? Could i use one light to do it all?(since that would be cheaper than buying two lights)

For my area and number of plants i wish to grow would i need more than one light? How powerful of an HID light would i need? Could 1 x 1000w HPS be better than 2 x 400w HPS?

On my first grow i only used CFL's so I really dont know anything about HID (HPS or MH) lights besides that they are better... I dont even really exactly know why they are soooo much better.

Any help from all of you professionals out there would be most appreciated!!
thanks,
frozen