Personal preference, but I have the B+W UV to protect, then Lee filters for the other - I leave the adapters on the lenses all the time and use Lee lens covers to protect from dust etc. Not sure if this is possible on other systems (e.g. screw), but you can independently rotate 2 filters on one of the Lee holders, so you can adjust perhaps for a bright sky, and perhaps tame a bright element in the foreground which needs a different angle.
90% of my filter needs is done by Grads (the rest is Circ or ND). I've done hand holding, but for long shots in the cold it's a little more awkward so I prefer to remove the gloves, add the filter/holder and then I can normally tweak with the gloves still on.
For the 10 stop ND, I could not work with the B+W ones as I'm always fine tuning composition (angle & zoom), so screwing on a filter at the end did not work for me.
Horses for courses, but prefer filter holders / drop in filters. The Lee glass filters are supposed to have less colour cast, but tbh, not really noticed a strong one on their resin ones.