I would prefer t5. First, the initial cost is quite cheap compared to those high-end leds and its only those high end leds that can illuminate a tank decently. Second, i find that t5 brings out the colours in corals better than leds. Third, there are many different types of t5 bulbs on the market that is readily available. The bulbs also come with the chart telling u which wavelength it peaks at. This can tell u how much of the light that is emmited is actually PAR. Another confusing thing is the heat output. LEDs still produce heat, but in unlike MH or t5, the infrared radiation is very low. That means that when u put your hand a distance away from the led fixture, your hand doesnt feel hot...unless its from the singapore sun. However, when u do the same for a MH fixture, your will feel heat. BUT, when u touch the led fixture, it'll feel hot. Because the leds conducts heat. Im sure those lumenaqua rgb or ultra brite users will know that its hot to touch. Thats also why u need those four fans to cool the fixture. The leds can also still heat up the water through convection. But it heats up the water much less than MH or t5 fixtutes