There is no best tool. I recently cleaned my cousin's PC. I used Emsisoft Emergency Kit, then ESET Online Scanner, then Malwarebytes, then HitmanPro with 30 days trial activated... and still the PC was infected with a persistent adware (iStart if I remember well). Finally, AdwCleaner finished the job, but there had also been some trojans there, which EEK caught first, and maybe MB caught something serious like that too, I'm not sure now.
The point is each tool I mentioned is great, but in this case each had a little more to detect, even 360 Total Security found some more unhealthy files and system settings, and that's the AV I left there for him after scanning with everything else. HmP found malicious proxy settings for IE which no other found. And so it goes, there is no single tool that can do everything. But fortunately we can, and should gain a lot by, discussing the best tools, plural, because if you're in trouble, you're probably gonna need a whole bunch of them.