To this day I have never played a Halo game. It's weird. I've played Wolf3D, DOOM, DOOMII, Duke3D, Strife, Heretic, Hexen, Quake, Quake III, Arena, Unreal Tournament, etc. I played Goldeneye a ton with so many friends. I figure if Halo was so great I would have run into someone playing it at some point IRL.
There really is no question who is more influential. GTA has been the focus of multiple controversies across the years, giving it the edge in political/media attention. No Jack Thompson types caring about the generic space marine in Halo. It is irrelevant. Robbing hookers, hot coffee mods, that kind of stuff gets the media excited.
Additionally, the third game revolutionized the Open World 3rd Person genre. It basically invented Open World 3D games. Yes there were 3rd person games before it, but afterwards, the idea of a simulated world was in a whole new paradigm. This is not something any Halo entry has done for it's genre.
I'm sorry, Halo is just a FPS. I get it, Xbox only has one franchise so they have to hype the hell out of it. But no.