Understanding what and how regularly you hope to scan might let you know everything you want to know about the attributes you might want. Photos and unbound documents are the most realistic items to scan, but you may even want to scan books, receipts, and films. Somewhat less popular are items like coins or flowers.
You might even focus on details like the highest size of the originals, and whether you might want to scan both sides of pages. That might make you know the type of scanner you might be looking at such as a traditional flatbed, a version with the sheet feeder, or something else.