Be honest.. although not always the cheapest.. Does anybody keep your credit card safer than Amazon online? And who wants to sign up for a new account with some random company. If the shit hits the fan, Amazon will cover me as a customer.
2. You're not responsible for fraudulent charges, so worrying about major retailers having your credit card number isn't really reasonable. I don't recommend saving your credit card in any store website. Enter it each time so they can't store it.