i've used cobs, quantum boards, and h.i.d., and theres a place for all of them.
cobs and quantum boards are great for a small scale grow, and even a large one, if the conditions are right, but even with the falling prices, h.i.d. is still way cheaper to get set up and running with, even if you have to buy a fan and some ducting to keep them cool.
if you live in a cold climate, at least half the year, you'll have to run supplemental heating with cobs or quantum boards, so theres a lot of your savings out the window.
as far as h.i.d. being more detectable to flir cameras...only if you don't set things up right. don't put your grow room right by a window, put your exhaust in a place where its camoflagued, inside the carcasss of an air conditioner, run it up the roof to your chimney or the exhaust for your furnace, or just hook it to the dryer vent, all easily explainable sources of heat.
more people have been busted with h.i.d. because more people use h.i.d., its been around way longer.
and heres the bottom line for me, i get bigger buds using a h.i.d......not saying better, not saying you can't get good yields from cobs or quantum boards...but i get bigger yields from using high pressure sodium than i did when i flowered under cobs or quantum boards either one. the quantum board weed was awesome, rock hard nugs that were just covered in trichs, but the same pheno grown under the hps produced 25% more. same conditions otherwise, plants were within feet of each other, fed the same feed. the quantum boards plants were ready a week earlier than the hps plants, but in that week, they produced 25% more final weight than the QBs did.
so what i'm saying is there's a place for both, and no reason to hate on either.
pick the one that seems to fit your needs. i know the op is growing in a closet, so in this case i'd actually recommend quantum boards, they use less power and produce less heat, and they also take up less overhead space.
that way you can avoid the extractor fan and ducting, although to be honest with you, unless you live alone with no neighbors close, smell WILL be an issue, so you might want to look into getting a 4 inch fan and a good carbon filter anyway, not for cooling but for odor control