I have been using Surfaces since 2012 with the default Windows Defender, never an issue. If you frequent Dodgy Sites you may need an Industrial Strength AV solution. I occasionally scan with another product just to double check and nothing has ever been found (I do this regardless of what primary AV product I'm running).
I don't have any issues while my dad (who clicks on everything because he doesn't know what it is) and has run various products for his Primary AV solution is always getting toolbars installed, and dodgy crap although he's never had a virus or anything that's officially malware but some flagged as PUP (potentially unwanted program). Even with his Admin privileges revoked
So if you have gotten viruses you might want to be more careful