Older design, single source scanners seem to work better than newer, multiple-lightsource models. Dedicated scanners also seem to work better than multi-function devices. Just a couple of generalizations from my limited experience that may or may not be accurate.
Almost all the pics of coins I post here on the forum and in my CCF gallery are done on an old HP single-source scanner (model: Scanjet 3770). It works well enough on coins in 2x2s, but I've never tried it on a slabbed coin, so I don't know how well it works on them.
Don't say "infinitely" when you mean "very"; otherwise, you'll have no word left when you want to talk about something really infinite. - C. S. Lewis