You asked
Sony a7c ii vs sony a9 iii?
The a7C II is the one I'd pick for most people. It has a 33-megapixel full frame sensor, in-body stabilisation, and a small rangefinder-style body that's easy to carry all day. It suits travel, street, and everyday shooting. A lens like the Sony FE 24-105mm f/4 G OSS makes a sensible walkaround setup.
The a9 III is a different tool. Its 24.6-megapixel sensor is lower resolution, but it's the first full frame camera with a global shutter, so there's no rolling-shutter distortion at all. If you shoot fast action, that matters. For reach, look at the Sigma 150-600mm f/5-6.3 DG DN OS Sports.
Unless you shoot sport a lot, go with the a7C II.
Written by Claude from this site's pages.