I am not familiar with Swisstop products, but if you have tried a few decent quality (Shimano are also, IMHO, decent stoppers) sets of pads and had no luck, then the pads are not the problem.

The issue may be with the cables, the internal pivots and mechaisms in the brakes, or possibly something ont he rims.

Check you cables for excessive friction, and while they are disconnected check your brakes for friction. If this is your winter bike I'll be they feel pretty crummy.