Neither are anywhere near to being as damaging as people would suggest ...
While over time pirates can become consumers, they are not going to purchase the kinds of games they're downloading in the quantity they're downloading them at if it became impossible to pirate them. I wouldn't be surprised if for every 100 game downloads only 1% to 5% of the people would buy the game if they couldn't download it.
With used game sales I could be wrong but I believe that most of the people who are selling their games used are doing so in order to buy another game new. While there would be some lost sales due to the (massive) cut the retailer takes, for the most part used sales act like a flow-through system that ensures the same number of new games are sold. Once again, I wouldn't be surprised if game sales only increased 1% to 5% if you completely eliminated used game sales.







