If you are looking for a 'fair' way to distribute something, I think it would be near impossible. How could you account for the time someone spent off-line working on their articles? Simply counting the number of posts is also misleading as many post a lot of junk content and they should not be rewarded for consuming resources for junk.

I feel bad that I'm not able to give any suggestions and can only provide more 'obstacles' for you to think about.