Honestly, a bass light headphone isn't necessary to kick ass competitively. I recommend a well balanced headphone. They don't have to be lacking in bass. The DT880 and Q701 are good examples of headphones with bass that still has great detail in everything else.
A bass heavy headphone is more enjoyable for non-competitive purposes. However. just because it's bassy doesn't mean they wouldn't do well competitively, hence why the D7000 and DT990 are two headphones I don't have issues with online.
If you find yourself playing online competitively a lot more than by yourself and non-comptitively, the I'd say get a well balanced headphone.
If you're like me, who plays mostly offline, then a bassy headphone would be my first recommendation.
If you can afford one balanced, one bassy, then you have all your bases covered.
Edited by Mad Lust Envy - 3/12/12 at 3:34am