I've run MH, HPS, LED and Flouro for veg.. Flouro's are no slower and no faster than MH, but they use a shit load less power, are less aggressive on young plants, and kick out zero heat. For me, that's a no brainer.I'm not into paying good money for lighting then paying to run a heater as well, if your in a cooler climate you'll be happy with the heat from hid, atm I'm toiling to maintain 25c above the canopy and 20c below it where the inlets are.
Fluorescent light are OK for seedlings or rooting clones when there's no rush, they're so slooowww lol give me a mh any time.
I think my led will be good for vegging where constant air exchange isn't so vital, it's low operating temperature isn't always welcome, horses for courses.
For heat in the flower room, in the summer, I'm more than happy not to have to run a jet engine sized extractor, and can keep my grow at a manageable temperature with an 8inch RVK running at 1/5th speed.
Something I've thought about now, is that running into winter I will be able to get by with even less extraction and that brings about the possibility of CO2 enrichment..