The lightweight division in mixed martial arts consists of B.J. Penn and everyone else.

We all know that Penn, the UFC champion, has established himself as the top lightweight in the sport. But after Penn, there are about a dozen guys who are practically interchangeable. That list includes UFC fighters like Penn's next opponent (Diego Sanchez), his last opponent (Kenny Florian), and some past and future UFC opponents like Gray Maynard, Frank Edgar and Sean Sherk.
And the list of lightweights who could make a case for being at or near No. 2 in the lightweight division also includes Dream champion Shinya Aoki, Bellator champion Eddie Alvarez, Sengoku champion Mizuto Hirota and Strikeforce champion Josh Thomson. So my list of the 10 best lightweights in MMA is basically B.J. Penn and a toss-up among everyone else.

Top 10 Lightweights in MMA
1. B.J. Penn
2. Kenny Florian
3. Shinya Aoki
4. Eddie Alvarez
5. Diego Sanchez
6. Gray Maynard
7. Frank Edgar
8. Sean Sherk
9. Joachim Hansen
10. Mizuto Hirota