I agree with Mr. Alberta...
One can argue the difference in output of MH vs T5, but the serious thing to consider is which will be best for your application. T5's are good for long and narrow tanks. MH's are good for lighting multiple "square like" areas.
one serious consideration is with my T5's, NOTHING could be kept in the upper 8 inches of my tank without it bleaching. I'm suspecting if I had a two bulb MH setup, I could have placed corals at the top of the tank, as long as they weren't directly under the bulb.
Comparing MH's to T5's is like comparing apples to bananas, and you really have to think over the needs of your tank before you make your decision. They're both great, they're just so different.
I liked my T5 setup, but I feel if I had a MH setup, I would have liked that too. Oh and don't stress too much on bulb choices either, because you'll get to try something else in 6-12 months anyways
