I have t5's but I have seen MH and they are nice...with such a deep tank the MH might be the better way to go...I don't like the idea of the excess heat as mentioned earlier so I am happy with t5's MH are of course more expensive and I imagine the bulbs are as well.....also, the MH guys can chime in, you may need a chiller to keep the tank temp low if the lights are going to be in a canopy? So, more $$$....unless you can have them free hang above an open tank....then I guess the heat goes in your room? anyway, I think the biggest issue, if you are not worrying about $$, is checking the depth issue and if you have to have MH to get light to the bottom (what will be on the bottom...something that needs bright light...claims?)