To kick things off, let me say there are no winners or losers. This is like a competition between toddlers at pre-school where everyone gets a prize. This isn’t a direct technical comparison between the two and it isn’t about proving you should buy one in particular. This is about guidance on how I made the choice between the two.
The Sony 70-200mm f/2.8 vs Sony 100-400mm f/4.5-5.6 is a common problem choice in cameraland particularly when it comes to sports. It’s not really as simple as putting a converter on the 70-200mm and putting them side by side, they perform differently with and without the converter. For me personally, the 100-400mm was my answer, but like anything, it isn’t the same answer for everyone, hence the reason this isn’t a one paragraph article.