I am in europe, so i use euros for impromptu and bar-work. For more formal work i use halfs and pennies. Euros and new american coins are just too small for stage-work. When a customer pays me a lot of money for a show a trick with some loose change just does not look right. The silver and copper coins add to the mystery, they look much better. If anybody asks about them i tell them i inherited them. Same with C&B, paper cups in the pub or coffeeshop work just fine, but i use shiny brass or silver for the better jobs, simply because the customer expects a magic performance. I would advise you to go for half-dollars, the gaffs are relative cheap and the coins are easy to handle, even with big hands. The power of using ordinary coins is that you can borrow them, but that is not easy nowadays because people don't carry much cash anymore. And then you are that guy who does tricks with borrowed coins, cool. That is what the audience experiences.
If you pull out a purse with a few large silver or copper coins and you do exact the same trick, they see you as a magician who does some serious magic. You have to be good, otherwise you wouldn't use those coins. This sounds crazy, but that is the way the spectator thinks.