You asked
Best telephoto lens for the sony a6700?
For the a6700, I'd start with the Sony FE 70-200mm f/2.8 GM OSS II. It's the most capable of the telephotos here, with a fast f/2.8 aperture that's good for sport and low light. It's also a big, expensive lens, so it's worth it only if you'll use it a lot.
If you want more reach, the Sony FE 200-600mm f/5.6-6.3 G OSS gives you 300-900mm equivalent on this body. For the longest reach of all, the Sigma 60-600mm f/4.5-6.3 DG DN OS Sports goes to 900mm equivalent, but it's heavy.
On a budget, the Sony E 55-210mm f/4.5-6.3 OSS is a light, sensible choice that gives 82-315mm equivalent.
Remember that the a6700 is APS-C, so every lens frames 1.5 times tighter than its number. For more on what to shoot with these, see wildlife and sport.
Written by Claude from this site's pages.