My official answer is: neither. I don’t use a thimble in the usual way–I need a “puller” or gripper on my right thumb to grasp the needle shaft so it doesn’t wreck the fabric when passing through, and I need a guard on my right ring finger because that’s the finger that I push the needle with when coming up through the underside of fabric. So, metal thimbles are just not workable. They are rigid and sit wonky. They also slip around or fall off. The leather ones are uncomfy and never fit properly. Being a “6-footer”, I have lo-o-ong fingers, and even large thimbles are never more than an inch or so long–which is WAY too short. So, staying true to my do-it-yourself ethic, I’ve invented my own. I use a standard yellow or green Rubbermaid rubber glove. Green is the thinnest, yellow a bit thicker. Both are great. Blue is REALLY thick for stuff like working on upholstery fabric or metal.
Simply cut out the best fitting finger to use as single glove-thimbles (glimble?), roll the thing over your thumb, and voila! A perfect fit needle puller that won’t fall off. It can be used on any finger that needs to grip. (The one above has been MANY miles with me–and the nature of mixed media stitch means it gets a little painty after a while–BONUS!) If I’m stitching a lot, I clip off the very tip for ventilation so my finger doesn’t sweat so much. I find the ring and pinky fingers of most too tight to use (but my daughter likes them as she’s smaller).