I'm thinking the OVZ and OVX are the most popular. I think drop lens lights are used on a far more massive scale than FCO. The OVZ, OVX OVH, and OVF are probably their top four lights though. Their OVY must be used some place too or else they wouldn't have kept it.
I'm not huge fan of any of the current Cooper fixtures. I liked the origial Cooper designs (the OVC, OVS, and OVM) but after than I really don't care for their fixtures too much. The L-150 and L-250 were actually designed by Westinghouse so they used all Westinghouse parts. the OVM and OVS used Westinghouse reflectors, refractors, and electrical components but used a different slipfitter and they were gray instead of silver.
The OVC was Cooper's "pioneer light". It was the first to use the current style rounded plastic refractor and the reflector with the circle imprints. The OVS contintued to use the original OV-15 style reflector, which is identical to the current cooper one but without the racoon eye cirlce imprints. The OVM used the same reflector as the OV-25 but when they replaced the OVM with the OVD/Y/F, they redesigned the reflector.
The L-150 as replaced by the OVS, the L-250 replaced by the OVM, and the OVC was just added to the line as a lower cost compact fixture to promote the use of HPS (since a lower-cost more compact fixture would make HPS more appealing). Then the OVC was replaced by the OVZ, the OVS was replaced by the OVX (in fact, the OVX and OVS used the same upper housing until Cooper redesigned the hinges in 2004-ish. the OVM was replaced by the OVD/OVY/OVF, a real change. The OVH/OVG was just added alongside the OVZ to offer FCO and sag lens optics, though the OVZ is still available in FCO to this day...
I wish that discontinued models could still be ordered from manufacturers. Like have a "1980s-1990s Throwback Thursday for the Whole Month of July" sales event where Cooper, GE, and AEL/Thomas & Betts/ offer lights from the 80s and 90s that have been discontinued. I'd order an OVS, OVM, original style M-250R2, and original style M-250A2 FCO.