Honestly I rather not have to use a chiller if I don't have to. And replacing bulb may not make sense if there is a fixture you don't have to. I am just looking for the best option for coral growth. I rather spend the money now.
With what lighting? If you are at 78-80 with fluorescent, you will be significantly higher in the summer with MH. LED is much more energy efficient, both in terms of watts/coral growth per dollar and in terms of not having to run a chiller or run your AC all day. MH is a proven entity. LEDs are still evolving (they seem to work pretty well, so far, but new twists are being introduced all the time and you may still need to upgrade (or at least feel the need to) in the future. LEDs probably will never need to be replaced in the lifetime of a tank, MH bulbs do, and they're pretty expensive.
Even with t5 u have to change bulbs... I would say got with LEDs. I have 2 Ai sol blues on my 57 and love them. No heat to the tank and cost less to run them. But it is a lil expensive at first but will save in the long run.. You can check my tank thread and take a look.
The AC would have to be running a lot to keep the tank cool under MH. A chiller is more efficient keeping the tank cool. But all that heat is transferred to the room with the added noise and now you have to run AC to cool the room.
MH have a really nice effect on coral growth but you pay for the heat and then pay twice to remove it.
imo, LEDs for sure. No heat, so no chiller necessary and no changing bulbs (50,000 hrs). Saves on the electric bill as well. MH bulbs are around $50+. Price is upfront, but you save in the long run as others have said.