Overall, O.E. tires are a mixed bag. Manufacturers want to cut costs, so they use tires that are cheap in bulk. Some cars (e.g., some Saabs) come with summer tires, which are useless once snow falls. But if you look at top makers, or "enthusiast" cars, where price is not the main object (e.g., Porsche, BMW), you can assume they've chosen a tire that performs well in lots of conditions and is a good, safe bet. (Many top makers use Michelins.)