I, too, used Avast for many years and then got fed up with ads., too much RAM and slow shut-down.
Changed to Comodo for HIPS, A?V and FW, regained ~300MB of RAM, programmes opened faster and shut-down is now 4 - 5 secs.
Tried Avira -heavy; Kapersky, similar and a couple of others. Trouble is, most need a separate FW and that's also a difficult choice - usually run Comodo FW without A/V.