I would say eBay just based on the protection from Paypal.
I seem to remember from a thread here that sellers on Amazon have little or no protection when using Amazon payment.
It is supposedly easier for a buyer to file a chargeback on Amazon.
Read the parts under:
Fraud, Disputes, Chargebacks, and Protection
https://payments.amazon.com/sdui/sdui/about?nodeId=73479#fdcp_how
Paypal's protections are a joke as far as I can tell. You can follow all their guidelines and still lose a claim to a fraudulent buyer.
I refuse to sell through eBay any more. As I've stated above, I've sold items "as-is", "Broken" with other various descriptions and pictures clearly showing what they were getting. In the end, they still file a claim and win every time.
I've also sold higher end PC parts on there, only to have completely different items returned and paypal/ebay always sides with the buyer. I started having a 3rd party (UPS Store, Fedex Kinkos, etc) pack and verify the items thinking that would help in the event of this happening again but nope. They still sided with the buyer and I lost even after providing them documentation from the 3rd party shipper that items returned did not match what was shipped.
Most of the people I've spoken to at my local UPS Store and Fedex Kinkos say this happens all the time. Their shipping sales are way down because many sellers have stopped selling on ebay due to the high rate of theft/scam.
Some people seem to like selling on ebay, until that one time you really get taken. After that, most just swear them off and deal with craigslist morons.