Metal Halide Questions

Wow, I am not sure if I want to touch this one.   Just like any piece of equipment, you are going to find a lot of fans of this or that.  To be honest, a lot of it is subjective and I encourage you to go look at as many setups as possible.  Thus another reason why it's important to go on the GIRS tank tours!
The first thing you should probably do is determine the wattage you are needing.  Usually the corals you keep and the size of tank will help determine it.  250W is probably the most common and you will find the largest selection here.
As for bulbs, it depends on the PAR output you need for your corals and the color temperature you are looking for.  Sometimes you will find it in a double-ended bulb and sometimes in a single-ended bulb.  The combination of bulbs and ballast will also play a big role on the output so choose your ballast wisely as well. 
Reflectors are another key component.  Spider light reflectors are antiquated by today's standards.  There's a few out reflectors in the market that will give you better spread and higher output.  Below is a link to lighting related articles written by Sanjay and his lighting configurator.  It will give you a ton of insight to lighting. 
Sanjay Joshi
Lighting configurator

 

Great answer!  That second link has great info.  Thanks for sharing!  I'll put that link into our Wiki.
--AJ

 

Why does a Lexus cost more than a Toyota? They share the same chassis. They are essentially the same vehicle and it will get you from point A to point B.

It's all about the brand and features. A brand like Ice Cap is a premium brand due to its long-standing reputation for quality and service. It's not the cheapest but you know you are buying something that should last a long time and service, should you need it. Coralvue ballasts is cheaper and probably has similar output. So why would you pay more when you can get something similar that will do the same job?

 

Just remember, in this hobby you tend to get what you pay for!