I prefer to play my video games alone, since me and my friends all tend to be "That Guy" when we hang out.
For example:
I play mainly RPGs and I'm pretty good at them, since I tend to figure out the meta game of numbers quickly
Another one of my friends plays mainly strategy games, Starcraft 2 and Rome: Total War are his top two played games, and he is pretty good.
Another friend of mine is really good at shooters.
Here's how a typical game session goes if we hang out together.
We'll play a shooter, friend 3 dominates me and friend 2. Only friend 3 is having fun. If we Co-op, Friend 3 ends up carrying us, and is having less fun because he's being brought down by us.
We play a strategy game, friend 2 has all the fun, and the rest of us suffer. We team up, everyone suffers.
However, if we play a new game together, than it's fun for all of us. Mainly because noone has learned the level layouts, strategies, or the mechanics entirely.
It's one reason why, though I enjoy playing Perfect Dark, I dislike playing with friend 3, because he has memorized EVERY SINGLE MAP. It's like playing against a Perfect/Dark Sim. But when he first got Unreal Tournament 3, it was a blast because it was a new experience for both of us. A week later though he had half the maps memorized, and it was significantly less fun, since he had played it nonstop for that entire week, and I was playing it for the second time.