There are two kinds of bullseye targets we use on our range: hunter and field. They both have concentric 3-4-5 rings, but the only thing you can really see when you shoot the hunter target is the white 5 spot on a black background. The field target has alternating black and white rings. I have read studies that found that trad archers do significantly better on the hunter targets than the field targets, probably because the white dot on a black background is a natural spot and there are no other distractions.
Practice on the things you want to get better at. I want to get better at everything, so I shoot at flowers, pine cones, plastic bottles, all kinds of bullseye targets, and 3D animals. Particularly 3D animals, since that is what I want to compete at, and is the closest practice I can get to hunting. Shooting bullseye targets can give you a false sense of confidence if you want to shoot 3D, because in most cases, the top and bottom of the 3 ring will be over or under the 3D animal.