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I'd save as PSD, since I'd probably scan directly into PS, and PSD is fast and stores all information Photoshop receives. Depends on your tools.

PNG (and PSD and TIFF) can save as 16-bit. I've figured that would be pretty useful for scanning, though nobody seems to use it. It'd make the output quality better if you do any adjustments (levels, curves, brightness/contrast), I think.