I have found that on several occasions malwarebytes has jumped in first and saved my butt, just the other day actually i had saved a free mp3 site to my favourites hxxp://beemp3.com/ the next morning when i booted up my system malwarebytes pops up straight away to tell me that this saved favourite is trying to connect out, no warning from avast at all so MBAM terminated the connection, i then run a scan and let it clean up the rest as there were a couple other things that it found, cant remember what they were but was related to the same link.
I have installed free versions of MBAM onto about 20 family members systems and when i do manage to catch up with them i always update there systems and there have been several instances after running some scans for them that malwarebytes finds something and this is with avast installed on all of them.
So in short this is why i praise MBAM.