Which is better - the man or zone blocking schemes? I can't really say one is better than the other. A combination of both is really the best recipe. Zone blocking is certain situations allows the offensive line to pick up anything, so if you're expecting a creative blitz you step into your gap and take whatever comes to you. It can be a very safe play. If you're doing man-on-man blocking and they run the right blitz with a run stunt it can really screw you up and actually lead to a loss.
So, it's third-and-2 - what do we want to do here? What are the defense's tendencies? There is a lot more that goes into that decision, not just, "Hey, let's zone block this." If you look at different tendencies of teams you pretty much know that, "Okay, in this particular situation this defense is going to pinch on third-and-2 inside the 30-yard line, so we might want to run a regular power play and pull the guard around. If we know they're going to play head up they might do the "G-play," which would allow the tight end to get a good block on the defensive end and either the guard or the offensive tackle pick up the end."
Is there a perfect one in the whole grand scheme of things? No, I'd say a culmination of both is the way to go and the best thing to do. If you can get your players to do that you've got so much in your arsenal that it will allow you to be successful at any point. The basic man-on-man blocking has its positives, but it can stall you at times if the defense is bringing very extensive and hard blitzes. The best way to answer it is zone blocking is kind of basic, but it can be kind of hard to learn if guys haven't done it before because if kind of breaks the rules of what you've been taught before. If someone knows you're a complete zone team they know they have to beat the double team, and if they beat the double team they win. In a man-on-man scheme it gets harder to pick up extensive blitzes or "bring it," which is basically taking the whole offensive line and bringing it to the right to pick up whatever comes to you. If you don't understand those concepts and are just man-on-man you won't be able to pick up those blitzes to help in a zone-type scheme.