Vizsla are smaller than the other two, and always have flesh pigment and usually a docked tail. They're also a sporting breed. Ridgebacks have a ridge down their back, of course (though some are ridgeless), and normally have black pigment. Coonhounds definitely have a more houndy build than a Ridgeback or a Vizsla. Their ears are quite a bit bigger, and their head is a bit of a different shape. They sort of remind me of bloodhounds, but with less wrinkles. There's probably more differentiating features, but I can't think of them at the moment.
redbones don't always have long ears, in fact a lot of field bred hounds have short currish ears like a ridgie or a BMC. ridgies don't always have ridges.
redbones almost always have hound heads which are almost always rectangular, while ridgies & vizlas almost always have square heads. also the vizla & ridgeback generally have a broad chest while the redbones almost always have a deep chest.