[Myka]

If you don't want to be limited at all go with an 8-bulb T5 fixture (or halides), otherwise a 6-bulb fixture of a mid-quality brand (like Tek) would not limit you much at all depending on your experience. If you are able to keep stable, pristine water and provide optimal flow you will get the most out of a fixture. Either T5 fixture would limit you to keeping high light corals (like SPS) in the upper third of the tank or so because T5s don't penetrate the water like halides do.

If you decide to use T5s, be careful with bulb choice. Buying a fixture with bulbs is usually not the best idea. Actinic bulbs are often very low output, and you would be better off with blue (20-22,000K) or blueplus (20-22,000K plus actinic) instead as they have higher output. T5 bulbs need to be replaced every 6-8 months for optimal output where halides will last 12 months. A good mid-range T5 fixture is Tek. I wouldn't want anything less with a 24" deep tank. VERY important with T5s is reflector quality and heat. Cheaper fixtures will use a single reflector and no built in fan. Without individual reflectors and a good fan to keep the bulbs cooler T5s lose a huge amount of efficiency and no longer function to any impressive standard.

Imo, nothing touches halides with T5 supplemental. If you want more info on halides ask away, but it sounds like you are leaning toward T5s right now.

Take a read through some of the recent T5 questions that have come up. I have offered up quite a bit of T5 advice lately.