I avoid the Norton/Symantec products like the plague. They are memory hogs, and almost impossible to un-install completely. Not to mention, expensive.
I use Avast Free. It's easy to use, updates often, and you can set how you want it to run. Don't click on the extra options, it will take you to the $$$ version.
I also use Malwarebytes Free. It doesn't run automatically, but it is easy to do manually. I do a scan about once a week.
I also use Ad-block Plus. Some sites want you to disable it, because they get their money from ads. That's OK, you can do it when you want. But it takes out a lot of annoying stuff.
The absolute best protection is to be careful where you click. Don't open links, or attachments, that come in email, unless it is from a known address, and something you would expect to get. Type in the address yourself. DO NOT play Facebook games. Don't look at porn. Don't click on any pop-up ads.