Some people want to be a noob, yet mainstream, and go mono-dragon. Everyone uses mono-dragon (unless you actually play Pokemon) because the only thing that resists it is steel, and thats a 1/all the types chance that you would see a steel type team (excluding personal preferance). Not only that, but a lot of dragon types are in OU, and better yet they are strong.
If you aren't talking dragon, you can pretty much use any type and do good. If you really want a challenge, use rock types without sandstorm or ice types without a spinner.
Other than that, there isn't any record of most used teams or anything like that (as far as I can tell)