I use the Martelli gripper ring. It's wonderful. I have arthritic hands and cannot spread my fingers or apply pressure without dire consequences. The ring has two knobs equidistant on the top. Your hands can be completely relaxed and the ring does all the work. It's hefty and it really grips. It's truly a blessing. Thank goodness for innovative people!
I should add, I have a Sweet 16, so there is considerable area in which to move the ring around. The continual re-positioning of the ring doesn't bother me; it gives me time to contemplate where I'm heading next. It also holds the quilt wonderfully flat in the quilting area.