Honestly, I have no argument for OpenNIC over Google's DNS that will convert you right now. It really depends on who you trust more.. strangers over the internet or a large corp who was the target of espionage. That's really up to you to decide the lesser of two evils.
A cool thing about OpenNIC is that they offer alternative TLDs that aren't part of ICANN's gTLDs. Also, the owners of the public servers strive to be as open as possible with their policies and features, such as no logging or using DNSCrypt. One of them even offers DNS level ad blocking, though I don't like it because I prefer the internet at its purest form and that policy doesn't seem to flow well with their anti-censorship mantra.