I am looking a used EOS E camera to be use mate of R50. Is 24 Mpix APS-C better choice than 22 Mpix FF?
The short answer is NO, a 24 Mpix APS-C would be about equal to a 15 Mpix FF, so a 22 Mpix FF would be a clear winner. Of course there are other things to consider apart from Mpix count.
Now I bought Canon EOS 5D Mark III sc 34 t. It is estimated it on my hands next tuesday, so four long days have to wait. What kind of choice this is?
5D series of cameras are great, and generally are considered a solid work horse FF. The mark 3 did have some people in the first few years have focus issues and send their camera back, so I would suggest with any used 10 year old camera that you put the camera through the paces testing it and make sure you have no noticeable issues before you are out of any return period. (I say this from experience of buying dozens of film cameras off ebay over the last 3 decades.) Otherwise i think you will love your camera.