In order to make the right choice in selecting a good document scanner, you will first have to determine its use, will it perform centralized scanning or de-centralized scanning. Centralized scanning means that documents are delivered to one primary scan station that serves the needs of the whole office; in this case you will need a larger, high speed scanner or simply a network scanner. In the case of de-centralized scanning you will need multiple desktop or departmental level scanners.
Then you have to consider the type of documents you will be scanning, some scanners have a limitation to what kind of documents they can scan. If you have a lot of document type that you deal with daily (A4, A3, Legal, etc) then it would be wise to select a scanner that has a diverse file scan type range and can accommodate different page sizes.
You would also need to determine if you need a black and white scanner or a color scanner, that would determine on the content being scanned. As far as the scanner cost is concerned, it is directly proportional to the number of pages scanned per minute. The more pages scanned, the higher the cost of the scanner. Here you should consider how many pages would you scan per day/month/year, if the number is greater than a scanner which scan a lot of pages quickly would be a good investment.
The most important thing to consider is the image quality, because at the end of the day you need a good image quality so that the documents being scanned are easily readable and understandable. Scanners that come up with an image enhancement add on will be useful here, along with the image processing functions that allow it to clean the document as it is scanned from inconsistencies. The lamp and optic technology also goes into play here, the better the tech the better the result.
At the end of the day, whatever scanner you may choose it must work with the default imaging/ document management software your company use. Most softwares will support an ISIS scanner driver or a TWAIN driver, the scanner hardware is built to work with either or both of the drivers. Make sure the scanner you will be using has the driver that is supported by the software package. In the event that it is not, a malfunction will occur.
And last but not the least, you will have to check the warranty of the product. Also check that does it have readily available parts and is it easy to get service from the manufacturer.