If your PC is fast enough & most even fairly new ones are then half the disc max is the general rule for a good burn (write).
Too slow can also be bad.
Of course a low quality media is not going to do as well.
I think software causing a poor burn is rare.
PC as above unless you have an older PC & its' processor is slow .
The PC won't be the problem.
Don't rely too much on quality scans . The real test is do the videos play well on your standalones . Is the picture quality good.
The final test is do discs you burned 5 years ago still play well.