To add to what wg said:
The laws of physics tell you that spot size is what determines sharpness. You can see this by scanning a reference target like the old 1951 USAF resolution test target. Scan at a bunch of scanner resolutions and you'll see that you get a maximum optical resolution that is consistent with the spot size. And spot size is aperture size.
So if you want the best in sharpness, you probably want the new Screen drum scanner. IIRC it's the only scanner on the market (that is, that's ever been on the market) that has a fully adjustable aperture size. This lets the scanner make an exact match of the spot size to the resolution you need, whatever that resolution may be. It should be very nice indeed.
Failing that, you should look for a scanner with at least a 6 micron aperture which will give you an optical resolution in the 4000 ppi range (depending on lots of other factors, like the quality of the optics). The high end ICGs and Azteks now have minimum apertures in the 3 micron range, giving an optical resolution that's something less than 8000 dpi. In comparison, the Tango has a minimum aperture of 11 microns IIRC.
The story I've been able to piece together from several operators and pre-press people is that the Tango was aimed squarely at the advertising and fashion market. It was a reaction to the Howteks, Screens, Optronics, ScanMates, and other scanners that were aimed at the smaller pre-press and short run press houses that couldn't afford the big Hell, DuPont/Crosfeld, and Heidelberg scanners. These new "table top" scanners were much cheaper, and more versatile - both were required by their target market. The Tango met the competition on price (sorta) and size, but was optimized for Heidleberg's traditional market of the advertising and magazine world. As such it was heavily optimized for chromes and for smaller enlargements (thus the 11 micron aperture). It's a marvelous machine for cranking out magazine pages, and the pre-press people just loved it, which is part of it's enduring reputation.
These days the vast majority of film scanning is by the the fine art crowd -- us. And we don't play to the Tango's strengths. Many of us choose to shoot on negative film, and I've heard that the software (currently called NewColor IIRC) was so optimized for chromes that doing negative work is a chore. Many of us want to make fairly big enlargements, and the larger minimum aperture of the Tango makes for large prints that aren't as sharp as they could be. What doesn't matter to a model's face on a magazine page matters a great deal to a landscape photographer who is after highly detailed and sharp prints.
The Tango is a fine machine when used as intended. All I'm saying is that it wasn't intended for the fine-art market.
Also, what would you expect WCI and NancyScans to say about their equipment? Maybe I'm a cynic, but I think you'll be waiting a while for any company to say that their equipment is anything other than the very best, no matter what that equipment is or what kind of a match it is to your needs. I'm just sayin'...