If you are interested in non
US coins and are considering ROI, specialize. Outside of a slab, knowing the diagnostics are very important.
I got burned out with US years ago and started on Mexico. I am not an expert, but have seen states' coppers go up 4x in the last five years, Iturbide 8Rs 2x. Gem Republic 8Rs bumped up a few years ago with China demand then slumped.
Overall, crown size coins seem to be the best bet. But if you like the coin, collect it.
If there is serious money involved, buy the book before the coin.