There are two PTC sites that I personally experienced, so I can only suggest you those two websites:-
1. The King of PTC sites- NEOBUX
This PTC site has paid thousands of users since 2008. As the name suggests, this is the most versatile and trustworthy website among all the PTC sites.
One can earn through it by investing as well as without investing in this site. Investing some bucks would boost the earning whereas without investment it would take the longest time to start earning. But I would suggest you start without investing a single penny in this site.
2. CLIXSENSE
This PTC site has paid thousands of users. Clixsense is known for its zero investment strategy to earn money through it.
