The original suits were made from ABS, and a lot of other armour makers use that because it's better than HIPS for trooping. RS are the first ones to offer PVC armour, and you are right in the sense that it is a super glossy kind compared to their ABS offering. But either plastic will not hamper you in regards to any awards like EIB and Centurion. Those come down to assembly and fit.
If you want something super shiny (some ABS can also be super shiny, like TM's acrylic capped ABS) or intend to do some massive trooping where it is more like rugby than standing around for pictures, then PVC would be a better alternative. If you want to do anything else, ABS and PVC are equally durable, and ABS the slightly more accurate material.
Basically it comes down to your own preference rather than any substantial difference.