We had a similar thread a while back:


Which lens? 100-400mm L IS or 300mm f4 L IS?


I think the 100-400 is better if you will take advantage of zoom and/or plan to use 400mm frequently.


I think the 300mm is better if you don't need zoom and/or don't plan to use it with 1.4X most of the time.


Generally, I think most people are better suited with the 100-400.