I have an Aquatic Life 6-bulb T5 HO
on my 75. I got it becasue I got a good price on it because it was mssing one bulb and the acrylic splash guard. I like that it has one cord and an integrated timer which handles the moonlights, a bank of 4 bulbs and a bank of two bulbs seperately.
On my 37 I'm using a Current 150W metal halide. It was on clearance from Drs. Foster & Smith and I wanted something to replace the DIY 4-bulb VHO
I had. I later added a single 24" T5 HO
strip I got on clearance from PetSmart to make it a little more blue.
The most efficient set up is going to be LED
. No bulbs to replace, generate very little heat and are very energy efficient. In a preconstructed unit, I believe you get what you pay for. The Marineland Reef Capable units are not what the name suggests at all. the top of the line seems to be the Ecotech Radion unit. It is dimmable, programmable, and you can adjust the spectrum of output. I will say I have read a lot of people rave about the value of the Taotronics dimmable units you can get through Ebay. Several folks have been successful with DIY kits from Rapid LED
LEDs can penetrate pretty deeply (if you get the right ones) and give a nice shimmer effect, plus you get all the energy efficiency with no bulbs to replace. the technology is pretty new and we'll likely see them get better and more affordable in the not too distant future.
T5s generate some heat, and are probably the least expensive in terms of initial cost. Bulb replacement is expensive (allow AT LEAST $120 per year) and there is no shimmer. they may not penetrate well in deeper tanks. You will likely experience some spectrum shift as the bulbs age. With different banks of bulbs, you can create a sunrise / sunset effect if you want to.
Metal halides cost maybe a little more than T5s, but give you a nice shimmer effect. They penetrate the water well. They are very energy inefficient and create a lot of heat that might need to be dealt with via a chiller. The bulbs will also need to be replaced annually for at least $50 per bulb. Although not apparent to our eyes, the quality of the light spectrum the bulbs put out can vary widely. The spectrum is also prone to shifting over time, going from (possibly) blue to white to yellow so slowly you don't realize it until you change bulbs. I think most people would agree that halides look nicest when they are supplemented with a little T5. Metal halides kind of have a built in sunrise effect as they warm up, althoguh it's only over a few minutes.
Ultimately, it's a question of budget and priority as to what you choose. If money was no object, I'd go with the Radion units myself. But that's a $1200 + investment all at once. . .