I agree that ODSTs always make the mission better and not only do they perform far better than the Marines, they also look far better in my opinion.
I agree 100%. We read so much about them in the books and it would be amazing to see them in-game. I just hope they don't mess up the character's A.I or make them act nothing like they really would in the books. I want it to be completely accurate to how the Spartan-IIs really are. I would also love to see the Spartan-IIIs make a comeback. For the Spartan-IVs, well, I'm not too fussed about them and I'm sure they'll be back.
I give my vote to the Spartans, preferably the Spartan-IIs/IIIs. I still think the ODSTs are great and I would be pleased to see them return.