Thanks Andy. I guess what I’m asking is, “is there a best or standard size to use” for most images? For example, according to StatCounter, the most popular screen sizes are:
1. 360×640
2. 1366×768
3. 1920×1080
If we use this example, wouldn’t it mean that, (if I want my images to look great a full size) I should upload at least a 1920 x 1080 image? My understanding is WordPress will allow me to select a smaller version of the same image (full size, large, medium, thumbnail).
http://gs.statcounter.com/screen-resolution-stats