Is it better to A: Take a coin photo outside on a sunny day, cloudy day, or partly cloudy day; or B: Should I use artificial light indoors adjusted as best I can? This would be for silver, clads, coppers and maybe paper money. I have a cool setup for my camera (not phone) that allows light from any angle and direction.
I prefer to use artificial light, and with 2 lights can control contrast and shadows. Since I use a heavy copy stand setup with an SLR, natural light would be a difficult proposition . Why don't you try both and post your results here?
Diffused light is usually better, using a thin white cloth (or even supermarket plastic bags work) over the light source to soften the shadows and give a more even light.
I have used several types of lighting. With a proper white balance, the images turn out about the same. Reveal bulbs seem to help capture color a bit better for me.
I use Ott-Lite white bulbs. If you look in Goodman's book you'll se he has measured their output as pretty much the same color and temperature as the sun.
Proof coins were giving me fits. I knew they were special cases, but I couldn't get things right. So I added a second Ott-Lite and moved them closer AND almost looking straight down. It's an improvement but I've still got plenty of room for more improvement.
sometimes i use sunlight to take pics of coins but most it's my 3 LED lights and a LED desk lamp (if needed)
A friend of mine uses his flatbed scanner to do proofs and slabs, they come out a treat, even lighting and great detail.