I have an Aquactinic MH/t5 fixture and I recommend them to you. The quality if excellent. I don't have any experience with the t5s for other than blue support but I'd think that you should at least, consider the MH fixture with the 175-watt bulbs. I think the wattage might serve you better for coral without any limitations.
Have you looked into the LED lights that are coming out or out all ready? I have seen them in action and they are pretty awesome.

btw, The unit I was checking out had clams being kept under the lights in a 120 and the clams where on the bottom of the tank.
Less power and you don't have to replace the bulbs for what appears to be a minimum of 14 years. I am sure that the price will drop eventually as the technology and bulbs become cheaper to produce.
Depends on a couple of things; what you want to keep, the look you want to give your tank (personnal taste), and the almighty dollar (how much you want to spend).

Do you have a canopy? Are you only interrested on fixtures only, can you go retro? Is heat an issue you will need to worry about? Is your tank a 55 gal regular (48" long)? If so, go with a 48" fixture.
The new PFO LED's are very kewl, they run extreemly kewl. I cn put my hand on top of fixture and feel room temp metal aka cool.

The light is very close to true hqi at 20k , the light however fails to fill the room w/ lite. It does however hit the sandbed fine to keep Croaceas.

As far as $ agreed ouch, but long term no heat generated into tank by light ( no need for excess fans or chiller- lack of bulb replacement for 15-20 yrs)

I have seen these run on friends tank for over 4 months she has as good of growth as i have w/ my 400w over 12" tall 60 gal.

just go read what Dana Riddle had to say on his fixture he tested

I think Sanjay will post his results after Macna

drill...The bulbs I got with the Aquactinic fixture are the Coralvue 14,000Ks. I have two Pure Blue bulbs with it. I'm confident that the t5 unit is a good one if it comes from Aquactinics. I'd just be certain that with the depth of your tank, t5 lighting has the sufficient penetration to light your tank sufficiently enough that you'd be able to keep whichever coral, clams, etc. that you'd want to anywhere in the tank that you'd want to keep them. I'm certain that you could do that with the metal halides but I'm not certain from my own experience that 195-watts (or 3.55 watts per gallon) would bring you into the range that you'd need to keep whichever coral you might want to try.