Both are good but have different characteristics. PVC is less rubbery and makes a very rigid tube, hypalon is positively bouncy in comparison. Hypalon will stand cutting abrasion better, eg. sharp harbour walls or barnacles.
For a sib, I'd choose PVC, it makes a firmer structure, hypalon sibs are a bouncy castle. For a rib it's not so important because the hull provides rigidity.
Personally, I find repairing PVC is easier since it does not require abrading.