I'm about to embark on a document archival process. I'm going to spend a lot of good money to archive some paper (actually microfiche) to TIFF images. I have a choice of 300-dpi bitonal (2-bit, black/white) or 300-dpi grayscale (8-bit). Cost is the same for either format.

Data volume (and thus image size) is not a factor.

It seems to me that the grayscale, since scanned at the same resolution as the bitonal, would always contain more information and could always be downsampled to the equivalent bitonal image. Are there any downsides to selecting grayscale, and then later downsampling to bitonal if desired? In other words, is it possible that the scanning software will perform a more accurate (or more legible) representation than a grayscale image converted to bitonal?