Malwarebytes Antimalware Free Edition and Avast Free have no conflicts at all or what so ever and it works perfect. I may not be too sure about the Malwarebyte Antimalware Premium and Avast Free/IS might have some conflicts or etc. Just wait for a better response.
Whoever that person told you that Avast & Malewarebytes conflict with one another is 100% bull crap, however you still have to exclusion your Avast software into your Malewarebytes and exclusion Malewarebytes software into your Avast because of the virus & malware database just in case of false positive between two software when scanning that all.
I have Avast Internet Security and Malewarebytes Premium and their is ‘NO’ confliction at all see my sig below if you don’t believe me
IF your not 100% sure how to exclusion between Avast and Malewarebytes correctly see screenshot below
I have one exclusion for MBAM Premium in avast:
C:\Program Files\Malwarebytes Anti-Malware\mbamservice.exe.
In MBAM the only area to exclude I would say is the area that avast uses to unpack and scan files:
C:\Windows\Temp_avast_ - this is possibly the area that could have an impact if MBAM is trying to scan files avast has sent there for scanning.
You could consider adding the:
C:\Program Files\AVAST Software\Avast folder though I haven’t got that.