If I were going to cop out and put a double header up like they did with Lionshead/Westwood, I would have gone with Looking Glass/Irrational, since many gamers wouldn't be caught dead badmouthing Thief, Bio/System Shock and at least there's some overlap between the personnel. Or maybe I would have said Bungie. People can bitch all they want about Halo's popularity being undeserved, but the bottom line is that Bungie honed their game design chops with Marathon and Mythic, both of which were easily first rate titles, the former being pretty much the single ray of light shining upon macs in the early 90s.
Ah well, it doesn't really matter. Ranked lists are silly.