Shutterbug Magazine digital Q&A column recommends Plustech as being the best available for a price people can actually afford. That leaves out the Imacons and drum scanners.
If my KM 5400 gives out, that would be my choice. Since I find his advice matches what I would give, I would tend to trust his opinion on things I do not know.
I am sorry I did not buy 3 KM5400 when they were available new. Used scanners are like buying a used car without an odometer.