Large image or small image
Large Images are better than smaller ones.
Since we use image renditions you can upload your crazy large images and when a user loads a page they won’t download that 20MB image that you uploaded but a smaller sized and pixel perfect rendition.
if you upload an image that is too small for the rendition that is needed, for example a very small image for a "Landing Page Header Image", then we need to stretch it out which makes it pixelated.
Small image uploaded as part of the header which is automatically stretched
Same image as above but with the correct resolution and rendition applied