If your computer specification allows you to select hardware acceleration (and you are not experiencing any visual problems) then we recommend to do so. The Best Quality mode is designed for systems where hardware acceleration is not available for some reason (either the GPU does not support hardware acceleration or it is not available for some other reason ex. driver problem). Best Quality provides high quality and smooth 1080i video playback with the cost of higher CPU usage.
There is one known situation when you may want to disable hardware acceleration and enable Best quality (1080i to 1080p conversion). We have noticed on some mobile chipsets slight stuttering of 1080i after conversion to 1080p. Enabling Best Quality helped. Best Quality has no meaning for 1080/24p content (it will look the same as in normal quality).