RS are the only ones that sell suits in PVC. Historically no other maker has used it so people's experience with PVC is very limited. That's why they recommend ABS.
I've built my TM in ABS and a friends RS suit in PVC. From a building perspective it doesn't matter which you choose.
From a trooping perspective it depends on a lot more than that. PVC is very nice and flexible which makes it durable. But ABS is also flexible and durable. With ABS it depends more on the thickness and chemical composition of the plastic since many makers use different suppliers and different kinds of ABS. For example, take 3 ABS suits, one from TM, one from RS and one from AP or ATA. Neither will behave the same, even if we had the same thickness of the plastic.
With PVC, since RS are the only ones selling it, you only have one choice.
The bottom line is that it doesn't matter as much as you think. Their PVC is glossier and slightly more flexible than their ABS. But other vendors, for example TM makes some very shiny and flexible ABS too.