I had the feeling that most people are going for UNSC. Those Mac Guns look Deadly... So I plan on going Covenant, unless I am mistaken on that.
MACs are deadly, yes, but the Covenant has a way of surviving. Quickdraw complained through our entire last game about my UNSC being overpowered against his Covenant, and he still won the game.
As a Covenant player, I would tell you to 1) use terrain to your advantage as much as you can, 2) take advantage of your 270-degree firing arcs (the UNSC pretty much ends up shooting straight ahead most of the time), and 3) don't pass up opportunities to HAMMER the UNSC's Marathon cruisers.