The first decision, whether to go with a mechanical ballast or a digital ballast is in my mind an easy decision. I personally feel that using a digital ballast is the way to go. I have done a fair amount of research and have used both types of ballasts in my own personal grows. The newer technology is the digital ballast and thus you get better results than its cheaper, older counterpart. Digital ballasts run cooler, are easier on the grow bulb, use less energy, and take up less space than traditional mechanical ballasts. Some manufacturers even claim that you get more lumen output with less energy use. I think it is worth it to pay a few extra bucks to get the better ballast, so I am in favor of digital ballasts all the way.
When comparing HID lights to fluorescent, or LED lights, you really want to look at the size of your operation as well as the environment you are growing in. Typically fluorescent lights work best for cloning and vegetative phases because the plants need far less lumens in those phases of growth. The fluorescent lights give off far less lumens, but also operate at a much lower power usage rate and much lower heat as well making it ideal for these phases of growth. LED lights are still too new of a technology to be worth the price, so at this point I would hold off using an LED light unless you have a very small micro grow with minimal space and small plants. Otherwise, HID lights are the staple of indoor growing and should be used during your flowering period and can also be used for vegetative and cloning periods as well.
From here, you just need to choose a hood that works best for your grow. There are a wide range of hoods available on the market today. The biggest difference you will see is the width of the hood. The width will dictate how much the light is spread out, so you really just want to find a hood that spreads the light around ideally in the space you will be growing in. It is also highly recommended to have a hood with ventilation fittings in order to be able to run your exhaust air right through the grow light hood.
These will be the main aspects to examine when determining which grow light systems are best for you. If you examine each of these aspects and you know what type of grow space you will be working with, you will most certainly get the best results out of your new grow light system.