I use Norton Security mainly because I use it on my PCs and it includes licenses for phones too. I primarily use it for the lost phone features. I'm not really concerned about viruses because, as of others have said, the chances are slim that you will pick up a virus via the Play store. From what I understand, even malware is screened out by Google for the Play store (or something like 99% of it is caught?).
Norton has some other features too... it will flag an app that is going to use a lot of personal data. It also has some backup functionality (I don't use it).
Just remember that security holes will come up regardless of whether or not your are using anti-virus software (e.g. stagefright). Common sense is the best protection. Don't open things from unknown sources is probably one of the key behaviors.