1/ Zemana: free, portable (but with some traces), fast speed, easy removal process. Not good great against brand new executable malwares (.exe) but extremely useful against already infected PCs, fileless malwares and PUPs. In default scan option, it doesn't scan Users folder so this should be scanned after the default scan. Very good detection rate which tends to be more updated than EEK
2/ HMP: free to use but only free to cleanup for 14 days. Slower scanning speed and slow upload speed. Very good detection rate and tends to be the most updated scanner out there. Very poor against fileless malwares but quite effective against new .exe malwares (which zemana is not good at)
3/ EEK: free, very fast scanning speed, very effective with the best detection rate but requires signature update, which can take some time due to large size. Very good against .exe malwares but doesn't seem to be the most updated scanner. It seems to be quite poor if the malware is brand new (<1-2 days). HMP and Zemana are more updated, IMO. Effective if the PC is infected after 1-2 days
4/ Malwarebytes: good against trojans, ransomwares and PUPs (maybe the best or second best against PUPs) but there is no official portable version. Scanning speed is OK. Poorest detection rate against regular malwares. Not recommended
5/ Norton Power Eraser: free, very fast scanning speed. It's like a file reputation checker rather than a signature-based scanner. Files with a low number of users and files known to have poor reputation will be listed regardless of their safety so it's extremely prone to false positives and can be dangerous if the user cannot distinguish which file is safe, which is not safe. Due to their low number of users, malwares tend to be detected by NPE although they are all missed by the other signature-based scanners. Very helpful but use with caution
6/ ESET online scanner: relatively slower scanning speed than all the above. Very good detection rate and tends to be the most updated, much better than EEK (in the first 1-2 days when EEK hasn't got the signatures for the malwares yet). Super effective against PUPs in default mode and a bit aggressive if PUP detection is selected
Agree. However, I would remove Malwarebytes Antimalware (and I have a lifetime license) as v3 has not been proven to offer substantial malware/ransomware protection (try and find an independent youtube video that adds to your confidence), and continues its childish outrage against all IObit softwares. Malwarebytes Anti-Malware classifies many useful progs as PUPs and removes them without hesitation, or user approval.
Personally, I would recommend that everyone use Emsisoft Emergency Kit! This is now my favorite second opinion scanner by far! The close second is Zemana Antimalware and third would be Norton Power Eraser.
Everyone that I help always gets these free tools from me, because I have seen how effective these tools are in catching the 'bad stuff'
I use to be a large believer in Malwarebytes Antimalware. Like @Telos I too have a lifetime license/subscription, but V3 is not as effective as one may think it is. In fact, I wouldn't recommend using Malwarebytes at the moment. The low detection with the use of Malwarebytes is alarming.
Hitman Pro is great too! While you may only get a trial you can keep it on your computer long after your trial is done and use it. While it may not delete the malware or the 'bad stuff' after the trial you now know where the bad stuff is and can remove it with the other tools mentioned above such as with EEK, Zemana or NPE.
I couldn't agree more with @XhenEd ! Personally I'd use NPE, EEK, and Zemana as second opinion scanners! One could use them all, because well.... These are all second opinion on demand scanners!
In my personal experience:
2) Norton Power Eraser
4) Hitman Pro
Zemana: good combination of speed and detection rate.
Norton Power Eraser is also great, but it tends to have more FPs, so I would only recommend it for advanced users.
EEK seems is a bit heavy during update (like EAM) and sometimes is buggy.
Hitman Pro: good if you have an internet connection. But if you perform a right-click scan, HMP only scans the folder you select and ignores subfolders, which is a big disadvantage IMO.
Malwarebytes: only for scanning PUP/adware. I wouldn't recommended it anymore, even though I have a lifetime licence.