I would pick Marcus Fenix anyday over Master Chief for my favorite character any day. Marcus Fenix has a bad ass attitude and a chainsaw that allows him to hack enemies to pieces.
Granted I think Master Chief has gumption, but to go into a fire fight with heavy armor Marcus is my choice.
Halo 4 is Xbox's last stand. So Master Chief comes back for round four, but is it as good as when Marcus thought everything wsa done with the Lightmass bomb, only 6 months later to figure out that there is a lot more where these locusts came from.
I would love to know which game a gamer would like to play and which character is more "bad ass."