Either will be fine if the rail they're being mounted on is straight and true. The unimount will be more forgiving on the scope body if the rail is as straight as a Pringle.
Even steel rails of high quality (NF, Badger, etc.) will bend if they don't (almost miraculously) fit the receiver perfectly. Bedding rails is on factory rifles is something I do EVERY time. Custom actions typically are much better, though. Even factory actions where the rails/rings mount on the same surface (Ruger American, Tikka, etc.) are pretty decent. It's the ones like M700's and Savages, and old M98's that have two different bridge heights that are, for obvious tolerance reasons, harder to manufacture parts that fit exactly for. In those situations bedding the pads of contact make the rail fit without bending so either rings or a unimount are equally effective. If the rail is bent... well your first indication should be to bed it so it's not... but the unimount will put less stress on the scope tube in that situation than separate rings.
