From someone who has both lenses, I can attest to the tack sharpness of the 300 f/4. But I agree with the other posters that the versatility of the 100-400 outweighs many of the shooting environments you're likely to come across. I'm not a fan of the push-pull, either, but it's really not that bad, once you get used to it. It's more of a matter of adjusting the friction ring properly.


Go with the 100-400.