I moved from AVG to Avast. "In what way is it intrusive"? Whatever you surf, avast will jump in before you to have a little check up, you will see the little globe on the task bar spinning, it will update every day, sometimes more than once, and slow you down for perhaps a minute whilst it does so, the globe again spinning.
If I were to award percentage marks, avast would hit 100. It is as good as one can get.. imho.
...and free.