For having the smallest BTB map group and having the smallest vehicle variety (that are actually on the maps) Halo 3 is picked constantly in Big Team Battle. People once complained that Halo 4 was constantly picked, but now Halo 3 shows up every time.
I think Halo 3 should have to share a spot with Halo 4 in the last spot of Big Team Battle because they are the most recent games and because they are combined the most popular and drown out the lesser picked and much superior maps of Halo 2 and Halo CE.
The new break down would be Halo 2/2A in the first slot, CE in the second slot and H3/4 in the last slot. On an unrelated note Death Island should be added back in.