I think trustport is the best, i m using it and it uses avg, Bitdefender,dr web,virusblokada. It's crazy. It uses its own signatures too but i don't know how effective they are. But every now and then i keep updating it and even after short span of half an hour or so the update size can be around 10 to 15 mb. I had a usb drive badly messed up and scanned it using f-secure (which also use Bitdefender)on my laptop , no doubt it found a lot of things on it but it had left one suspicious file in my pen drive which by the look of it, looked suspicious to me, no matter what fsecure won't detect it. I removed the drive and scanned it with trustport and there it was detected. I don't know which engine detected it, but it works. It's a highly under rated security product which i think people should try.
PS: UI isn't that great in case of trustport.