What is the difference between Exclusive and non-Exclusive licenses?
Exclusive means that only 500px can license the image commercially and you have never licensed this content commercially before. Non-Exclusive means you can sell your image through other commercial licensing vendors, or directly to commercial buyers, or you have licensed it commercially in the past.
Which license is better for the Photographer?
Exclusive licensing provides a greater revenue opportunity for the Photographer and exclusive content will be featured more often by 500px. Exclusive content means only 500px can license this photo and you cannot license this photo to any other agency or make it commercially available to anyone else.
An exclusive image can be potentially licensed for "Exclusive Use", for a set period of time, for several thousand dollars in most cases. If a photo is licensed for this special "Exclusive Use" it can not be sold commercially to any other buyers during the time period negotiated. The photographer will earn 60% net of every license purchased.
Non-exclusive Licensing is meant for photos that have been licensed in the past, or you want to make available for commercial licensing through other vendors or agencies. These photos will earn 30% net on non-exclusive licenses purchased.