My absolute favorite Mythic would be the CE Magnum. Much nostalgia, easy kills, and fast reload.
Whispered Truth, reminds me of GoldenEye
Mine would have to be the Prophets Bane. Imagine your enemy is in a base (at least 6), and your in active camouflage in a corner they would past often. It is pretty funny when they start shooting at walls to find you. Plus its camouflage compliments the extra lunge range by disabling the motion sensors of other Spartans. Allowing you to appear out of thin pixels to attack your enemy. I find it a great weapon to harass your enemy with.
Partial to sniping, so Nornfang