What would “best inner bags” mean, just the quality of the bags or something more? Well, since plastic side cases very often have irregular inner shape, in my opinion, optimal space usage is as important as the quality. Instead of the further explanation, let’s see the internals of the BMW touring cases:
BMW offers good quality inner bags but according to the pictures and forum’s opinions I could find online, they do not occupy all internal space. This can be good in case you want to add some additional items like rain clothes, but these small items may also very easily fall out of the cases when you open them so my conclusion is that it is better to use the whole internal space of the side cases by inner bags and keep all small items in the top case.