You should be safe either way. Paypal isn't about to go taking things from your accounts. However, if you are concerned about hackers getting into your account or something, then a credit card would be safest, as all a hacker might get if they did manage to get in (Mind you, this is a next to impossible occurance so long as you keep your login information very safe and secure) would be credit card information, and you aren't liable for it. Really, as long as you plan on keeping your login details hidden and hard to guess, you can safely use either a credit card, or debit card/bank account.