Depends on the specific product, the mold maker, and the plastic injection facility. In general, it seems like North America is able to produce the regulated products (i.e. medical & military) at a high quality level, but with some limits as to the specific media (plastic types), colors, and tool designs, and at a high cost. PRoC has a wide spread of providers, and quality is not well-correlated with price, so it really depends on who you know, but you can get very good parts of all types at very appealing prices, but communication is terrible, delays are common, and quality can drop sharply from one run to another.

Overall, I've mostly given up on North American producers because I do pro-sumer products, and they're too expensive and inflexible for me, but we're also fairly low-volume, so it may just be that I don't haven't had access to the right providers.