Who knows? They each have their own benefits. Some have innate scanning abilities within zip files and across your local network. Some operate within your system ram checking every single process for “virulent activity” – warning you if any application ever does *anything* that is “questionable”.
Unfortunately – every application has “questionable behavior” every once in a while. In fact, any major antivirus program will tell you that it gets false positives all the time for applications that are just operating normally. The MS Office suite performs “virulent activity” so regularly that vendors have added the ability to “ignore” those applications from their warnings!
That said, my current preferences are for the “smaller” engines, because they’re less likely to risk their reputation with a huge mistake, like including a virus in their updates!