I'm all about course headcovers. My reason is simple: I don't want my buddies to know when I have switched out a club.
Yes, I like to tinker and I don't feel bad about it. But, in addition to usually being ugly and cheap, OEM headcovers scream that you have new toys in your bag. A club cover is more stealth.
And, frankly, a nice leather headcover is a nice thing to have.