I changed my mind... I also vote for option B: We consider the Top 5 (of each class) over all the BGs. -> (FW+CS+Skyring)/3 = rating
Because this way you will actually reward players that are keeping every battleground alive. And you will reward players that are not feeding with their undergeared alts because they are too afraid to que with main. This will also make games harder if more players will que with their best geared characters.
PS: Had some problems with account so I asked board admin to delete my old account. Was never banned tho. ;D
The idea itself is not bad, that simple show your knowledge about your class in all discipline (deal with mass pvp, grp fight, etc), but overall i would put skyring over CS/FW rating since it require more individual skill. (which should have a higher value)