There are a few aspects of coins that make them difficult to work with. These are:
1. Thick and thin coins. This causes the coin to wobble and distort while being made. These coins include silver quarters, Ben Franklin Half dollars, mercury dimes, and any high relief coin. The Swedish Wrap tools and technique is a great way to get around this issue. The 17 degree dies are still need though to start the fold and final shaping.
2. Reticulation. This is when silver gets too hot when annealed and can cause a bubbly skin on the coin. I have noticed a few coins that this can happen too easier than others. These are JFK half dollars, Ben Franklin half dollars, and silver Mexican Pesos. The trick here is to anneal in a dark room and only take them to a dull red.
3. Difficulty in getting money back from scrap and mistake coins. Silver and gold coins are the easiest to sell to a refiner or gold and silver scrapper. Platinum can be difficult, as well as palladium. If you can find a local refiner or scraper that takes these metals for a fair price, that is a great way to go. You can also barter with me for tools as well. I like precious metals. Honestly though, I see it as money in the bank. Actually, better than money in the bank, especially silver. Hold on to it as an investment if you can but if you need to sell it, find a place before you invest in a roll of platinum coins.
So the easiest coins are the clad coins we use today, silver Barber coins, and any other coin of a common metal and without a high relief.