I'd say a credit card, via paypal for sites you either don't trust fully or you only expect to use once or twice.
I use two different credit cards online, one purely for a very limited number of stores (3 that I use on a regular basis), and one that I use for other stores, although that one is also linked to Paypal so I can use that when it's an option and I'm not expecting to be buying from the site on a regular basis.
IIRC credit cards when used directly offer far better protection against things going wrong, as required by law than Paypal which can be very hit and miss as it's largely down to their internal policies.