What Ted said, they are all a tremendous value for what they are. I had bad luck with quality control on the Microteks, and the progression of Epsons I've had make steady subtle improvements. What is limiting is the crappy Epson software and I do need to try Silverfast. I've been using VueScan and it is too bizzare for color work (it's fun for B&W though!)
I'd save my money and buy Imacon scans for the big stuff. I perceive a subtle improvement between the 3200 and 4990 scans, but I am still working with scans from my old 1600 model that are fine and I don't feel the need to rescan old work because the scanners are so awesomely better.