VGking summed up the main points, but I think this may also come down to how much true developer talent Respawn have managed to carry over from Infinity Ward. COD4 is one of the most significant releases this generation, paving the way for the behemoth that is COD today.
Bungie, while admirably producing some great games, went from being the premier top selling FPS developer heading into this generation, to second place as a result of IW's efforts. IW also introduced many innovations and gaming mechanics that have possibly forever altered the way First person shooters are played and have spurred numerous other developers to adopt their ideas into their games. While Bungie innovate, I think IW did it more successfully and in line with what the market was looking for.
Both developers struck it big once and can definitely do it again. If I were to bet though, I'd put my money on Bungie. They have a more complete studio with years of experience working as a team and with Activision's massive marketing clout behind them, it's unlikely their future project will fail.
It's hard to rule out Respawn entirely though.
