I don't specifically like the covenant, but more so on the sangheili. I hate the jackals, brutes, hunters, and the drones.
I don't like the UNSC either, simply because they wouldn't stand a chance without the master chief, and that's a FACT.
One of the reasons is this: For me, grunts are easy as hell to kill, yet the marines and even ODST's have problems with only 2 or 3 of them. It's pathetic. You know what I mean if you play the campaign with AI allies who are human.
The covenant are cool with their vehicles and large spacecraft, it's awe inspiring.