Ok, so this is a long video (I hate doing videos, I really do) showing the method I use to get a ring to read consistently. There is a Mifare Classic card included for comparison, and I've also shown what can happen to read distance and quality merely by twisting the wires from the microduino uno to the PN532 reader.
To explain something with the rings, the smaller the ring size the more pronounced the curve of the inlay - this can also affect read quality, but using a better read method will compensate for this. Ring orientation will also affect how well and how far you can read the ring.
At the moment I don't really feel up to explaining RF propagation waves and why you get better read areas in different places but that is definitely worth looking at for at least an explanation of why things could be different for you. Proximity of other devices, metal, even your hand can affect this. I have a post here on this.
The bare inlays that came with your order should behave more or less the same as a comparably sized keytag or sticker. The lack of a metal surrounding lets them interact a little more readily with the RF field generated by the active device.
I believe silver isn't the best as it might be slightly reflective to RF, you'd have to ask @johnyma22 to clarify that. Black, transparent and white should be comparable in performance and behaviour.