Kelly. She has been with John from the very beginning: Witnessed his changes from unlikable brat to great leader to legendary war hero. She's been with him through thick and thin. They were together during Samuel's death. She made it through the bio-augmentation with John. She stuck with him throughout the entire Human-Covenant War before the Battle of Alpha Halo while the rest of Blue Team were pretty much interchangeable. She has a likeable personality; Dr Halsey mentioned her as one of the only Spartan IIs ever to regularly exercise wit. She is the fastest human ever known. How could you not choose Kelly?
Why must you do this to me!!!!!???!?!!!???? Ok, keep in mind that all these Spartans are within like a hair of each other in my book, but I'd have to rank my top as
Tom B-292: because he reminds me of a younger Master Chief. His character development is great. He is a great leader, good in combat, has a deep connection with CPO Mendez, he cares about his fellow Spartans especially Lucy, and he is sensable. The way he thinks is similar to how Chief thinks in other books.
Fred: I have said it countless times, and I'll say it again. Fred is the best Spartan. Master Chief says so himself for several reasons. Fred is so underrated in the series it hurts me. He is a legend in of himself, and the highest ranking Spartan-II.
Kurt: Kurt's personality in Ghosts of Onyx was amazing. He was so different from other Spartans. His 6th Sense had proven he is better than Chief. And in my opinion can possibly rally more hope and inspiration in his troops
Will: the dude beat a hunter in hand to hand combat! He grabbed worms by the fistfull and yanked them out!