Vasari all the way.
Come on, is it really any competition that the Vasari have from the Covenant? Covenant can glass planets, sure, but the Vasari have Kosturas (instant door to the enemies primary planets), Phase Missiles (shields? Those were shields? I didn't notice them), and they've got the Egg, the Kortul (it's pretty good, just try it), and best of all, Gravity Mines.
Covenant flagship bridge-
"Truth, we have been immobilized by some kind of gravitational anamoly field"
Vasari Sivuskras Ruiners on com-
"Emperor, we have immobilized the enemy's fleet"
"Excellent. Our forces will be phasing in momentarily"
Ten minutes later-
"The enemy was absurdly easy to defeat. Their ships and weapons seem weak, and they rely on shielding far too much"