After trying many different filament clips, I settled on this one. It is a remix of https://www.thingiverse.com/thing:2817985. I only made it wider and rounded the edges a bit.
The advantage of this filament clip is that it doesn't twist or bend the filament. It won't interfere with other spools in the same box, won't come off by itself and will not twist or turn on the spool.
Attaching to and removing from the filament on the spool is easy and it allows you to tighten and slide the clip along the filament for a perfect fit.
The author hasn't provided the model origin yet.