KAV of AT is defnitly ewido. I can say that cause I guess I know both mentioned programs quite well
Comparing ewido and a-squared is kind of pointless. The idea behind both programs is completely diffrent.
Ewido put all their efforts in building a reliable and powerfull engine focusing in detecting known threats. Thats why ewido has a superior engine above all AT applications available currently - compareable to KAV in AV sector. Maybe their engine is even more powerfull than several AV engines out there.
A-squared is built around very powerfull heuristic based concepts. We never planned to have a reliable scanners - its more a gimmick. We put all our effort in building a system to detect malware without relying on signatures and other "old school detection techniques" and we surely focus on detecting new threats. Maybe we are DrWeb of AT
Sure we can scan files too, but we defnitly won't achieve such a high detection rate as ewido when it comes to file scanning only. On the other hand ewido has heuristics, but won't detect as many new threads generic as we do.
So if you want a powerfull file scanner that relies on strong file scanning abilities like KAV does, buy ewido. If you want a tool with a more generic and heuristic approach, buy a-squared.