We have T5's on our 120g tank downstairs and trust me after a year the bulbs need to be replaced, however the nice thing about the T5's is that it's cheaper to replace the bulbs. We have a 250w HQI MH Hamilton on the 30g tank upstairs and one bulb for it is the same price
as the 5 bulbs for the much larger T5 fixture. I have noticed a bit of a difference in coral growth between the two tanks (although all our lps and softies and aneomone are growing quite well with T5 lights) I think the MH provide a bit better growth rate then the T5's and sps and zoos do much better under the MH. On a personal note I love the overall look of the MH way better then the T5's. You wont notice much of a difference (other then the shimmer) between the two lights until you have one of each in your house to compare to, at least that's what I found.