Some of the ones that I have heard good things about include:
- Razer Deathadder
- Logitech G Series mice
- SteelSeries mice (There are 2 versions, Raw and Normal. Normal is more expensive, but has a few more features.
My personal favorite is the Deathadder, but make sure you register any Razer product that you buy on their website to receive the warranty, as Razer products are known to, erm, have a "low durability".
There is no "best" mouse for competitive gaming, everyone has different preferences and sized hands. What works extremely well for one person could be terrible for another playing the same game.
Watch this, use it to make your decision. http://www.youtube.com/watch?v=luCxbVslSFM