Antivirus in Macbook
I think you mean OS X, not iOS? MacBooks run OS X. iOS is the OS on iPhones, iPads, etc.

Some good, free antivirus options for OS X are Avast and AVG.

You're definitely safer if you use them. There are viruses out there for OS X. That said, it's not as needed as it is on Windows. I personally don't use any antivirus on OS X, because I feel that it slows down the system a little bit. I feel the risk is rather small, so I am willing to take it. 

It comes down to how careful you want to be. If you don't mind your system slowing down a little bit, and want to minimize the risk of viruses as much as possible, then get antivirus. If you don't want the small slowdown, are wise enough to spot obvious traps like fraudulent websites asking you to install programs, etc, and you feel the risk is small enough, then don't install it.