For static (non-rotating) filters, I have the best luck simply placing the lens face down on a grippy pad and twisting the lens. The grippy pad holds the filter in place and you unthread the lens from the filter.
For c-pol filters with rotating frames, a rubber strap wrench is often the only thing that will grab on to the knurled segment of the filter.
When you feel your filter threads getting a bit rough and resistant, apply the tiniest smear of instrument oil to the threads with a toothpick and screw the filter on a few times to distribute it. Just avoid glass. This will last a while and make life with filters better.
I bought mine in several sizes to fit my lens filters. They are metal with a rubberlike coating on the gripping surfaces. I've had these sets for about 7 years and haven't needed them for my filters yet, but I always carry the size with me that fits the lens and filters that I have with me, and I have rescued several photographers with stuck filters while out shooting in parks and other tourist areas. They have never failed to save the day for someone. I don't remember the manufacturer, but I bought them from Amazon. Many of my orders come from Adorama and B&H in New York, so I suggest that you try these sources. They weren't expensive and just one rescue would more than pay their cost several times over. Look for the metal with rubber coating versions. I think you will be happy with them. Buy the correct size for your lens and filter size. Don't force fit them to a size they aren't designed for.
