Pretty much anything that isn't Halo 4... I mean... Yikes... Personally Halo 2 had my favorite marine design. Mix that in with voice acting from David Cross and Michelle Rodriguez, and you've got the best marines in the series.
Halo 2 and 3's Marines looked best, Halo CE Marines where good but lacked in detail but its understandable for a game that's really old, Halo 4 and 5 Marines don't vent look like Marines, to me they just look more like a really cheap versions of Spartans and ODST