The Arbiter.

The Arbiter - being the leader of his clan on his home planet, is faced with assassination attempts. This is a tradition for his race (or at least the honoured ones).

He would have much better situational awareness from his own practise, he is skilled with and without a weapon, and, come on! Who wouldn't want Thel as their bodyguard, he's the frickin Arbiter!

Also he was Supreme Commander of the Fleet of Particular Justice - which makes him cool.

Where is Tartarus in all of this discussion? He's pretty beast too!

i would also rather the Arbiter but you forget that spartans are super soldier and The master chief has Been in worse situations than the arbiter his reaction time is super fast and he's a mark II spartan plus he's the best. but still i would rather the arbiter i have to admit if i put the arbiter in halo wars i would choose him but thel is still really cool.