iEchoic:I wouldn't recommend running 3 UNSC. It leaves you vulnerable to gremlins, whereas any Cov leader pretty much prevent them from being used.

This. It's always best to have at least one of the other Faction, should it be 1 Cov and 2 UNSC, or 1 UNSC and 2 Cov. It also depends how you want to play. If you're looking for a late game....game (olol), then it's probably better to have 2 UNSC. Obviously, that's not always the case.