If I could buy with bitcoins, it would be useful but since websites in my country offer discounts when I make purchases via cards, I would prefer them as I get about 10% less and if the same is available for bitcoins as well, it would be preferable. I've never tried PayPal as a payment option ever.
Bitcoin is safest to way to buy in online easily, as you said If you need good discount means you have go with Card way payment only.
Nowdays bitcoin also comes with some discounts in online stores like Ebay, Amazon, Cheapair and many more. So I advice you and all to go with bitcoin payment mode in increase the stability of bitcoin.