Don't expect to see much IQ difference between equivalent camera models. Its just not going to happen.
Look instead at lens prices and availability of good used lenses
Look for features you want or will use
Look for availability of third party accessories
Look at Service times and user issues
Look at prices
Look at resale prices
Try the product out if possible to see how it fits in your hands, and check the layout of buttons and menu screens.
We are all different and we value different things differently, so get whats right for you.