Really hard to decide as I like and collect multiple series. But I have probably invested the most time in the Trade Dollars. S/CC AU58:
Very difficult to pick a coin, or series. For now, I'll choose Buffalo Nickels. 2 minutes from now...?
If you zoom in on the goat, I think you will agree that the details and highlights/shadows came out beyond belief. These coins are from the 1st Perth Mint Chinese Lunar series. Bought them at the big coin show in Orlando in 2006 I believe, and they weren't much over spot as I recall. I wish I had the whole series but they have increased in value too much to pursue the others.
Thank you @Pickin and Grinin for showing Roosevelts some love! However, how are these not posted as of yet? Outlandish!