My necklace is a length of a soft webbing with a small basic biner. It was just knotted at first, but as I worried about catching something with it and being strangled, I replaced the knot by a plastic quick fastener from a back pack. I saw that they can let go if we pull hard enough on it. Not sure if my neck could actually stand that much force, but it's a bit safer. Plus, I made it a little shorter than the "pass the ears and nose" webbing loop, more convenient to hold the ascenders.
I was tempted at first by the lanyard over the shoulder, that's one less thing to carry in the tree, but the lanyard isn't available if you have some cutting to do during the ascent. Or if you are already using it for work positioning, you miss it to go up on the ascender. The chest roller doesn't appeal me neither, too thick, hard, bulky for my licking.