mogul screws in like a light bulb. HQI is a double ended bulb ... has contacts on both ends.
As for recomendations, I have always used and like Coral Vue bulbs. They are cheap and my corals grow extremely well IMO
. I considered Hamilton 14k's when I bought the CV's.
XM's are supposed to be nice too.
Not much help here but that is what I have used.
*180 gal Display, 100 gal basement sump, 33 gal refugium, 3x250 MH, 2x160 VHO actinics, zoos, some softies, LPS & lots of acros and other SPS.
*100 gal prop tank plumbed into main system w/ 2x96 PC lights and 1x150 MH,