MSE is all you really need. The bigger threat these days is malware. Malwarebytes comes to mind as one of the best for that.
But if you're technically incline there's always free Avast. For paid versions there's Nod32 and Bitdefender.
Avoid crap like Norton, Mcafee, and Symantec like the plague. Unless you're over 80, still have an active AOL subscription on top of your cable internet, or use internet explorer. Then... Well... Nothing is going to change your mind.