For 35mm cameras like rangefinders, where I won't be using any big heavy lenses, I like the Black Bag
thin straps. Really supple and not very expensive. Been using these on a Contax IIA and a Voigtlander Bessa-T. I also have a Voigtlander cloth strap
(bottom of page) which is great, but no longer available new. You might be able to find one used. For SLR's and some MF cameras, it's been Domke 1" gripper straps, with and without the swivels. They soften up quite a bit with use.