Revo, BCUninstaller and IOBit Uninstaller will all do a good job uninstalling most existing software and, if you use the ‘scan for left overs’ option or whatever the particular uninstaller calls its deep clean capability it will also clean up the registry too. You have to be careful with that though as ‘associated’ software can sometimes be wrongly included.
BCUninstaller will also look for ‘orphan’ items even after you’ve uninstalled the main program.
But at heart all of them just use the software’s own built in uninstaller and even with the ‘deep clean’ they can still leave behind stuff you have to remove manually.
With AVAST there is no inbuilt uninstaller, all you have is the Windows basic Add/Remove or Uninstall Program Control Panel option. IOBit Uninstaller actually adds itself to Control Panel menu and whilst it will do a better job than Windows itself the other uninstallers mentioned will work just as well.
The problem with AVAST is that it does not want to uninstalled even if you disable the self-defence module in AVAST’s settings. I suppose, with a security program, that is understandable where an obvious way to get at a PC for malicious intent would be to to remove or disable the AV protection by uninstalling the program or parts of it.
In short using any one of those uninstallers is likely not going to get rid of AVAST completely. You will have to use AVAST’s purpose designed uninstaller avastclear. in the way instructed (Safe Mode) or back it will come or reboot/restart.
https://support.avast.com/en-gb/article/10
What I don’t know, never having used it, is just how thoroughly avastclear cleans up the PC of all AVAST stuff.
Also whether it is possible to use avastclear after having used one of those deeper clean uninstaller programs. There can be a problem with leftovers, particularly in the registry, if they’re not removed at the same time as the parent program. There is nothing for an uninstaller like Revo to latch onto again once the main program installation has gone.
*If avastclear can still identify and remove everything still left over in such circumstances ie. after use of a deep clean uninstaller I would be interested to know.
I’d also like a little more certainty provided about the best removal procedure ie. assuming that the above* is OK is it recommended to use Windows/third party deep clean uninstaller first before using avastclear or simply go straight to Safe Mode and use that only? Which actually does the more thorough job?