Always scan at maximum optical resolution (2400 ppi in the case of the
Epson 2400/2450 scanners). This gives you the most flexibility in post
processing, including sharpening, downsampling, etc work.
The biggest advantage in doing the processing after the fact is that
you can un-do operations that reduce quality, where if you allow the
scan process to do the work, you're basically stuck with the image
presented by the scan as a baseline unless you re-scan it.
There is no fully automated way of ensuring best quality scans to date.
Many of the best looking photos on film require a ...