Difference between HQI, EYE, standard, and electric ballasts

[Josh23]

Thanks everyone for your input.

I was thinking along the lines of buying a 250 watt dual PFO ballast.
Not sure whether I would go HQI, EYE, or standard though.

Reason because the 250 watt dual ballast would allow me to ad a second bulb, reflector ect. later if needed. As I understand it a 250 watt ballast should allow me to keep just about anything including SPS and LPS, Softies as long as they are placed correctly in the tank. I wanted the ability to keep a variety of animals and prevent a upgarde later on.