On our previous two trips to Florida, we used American Express TC's just like cash and the stores give you cash as change. I don't like the idea of travelling halfway around the world, trying to use an ATM and having my card swallowed. Hmm - what would you do then? Its hard enough trying to get your card back in this country if an ATM doesn't give it back, imagine trying to get it back in a foreign country?!
Personally, I like the security of TC's, especially the American Express versions. If they're stolen or lost AmEx will replace them quickly. As I said, we've never been turned down using them. When we know we're going to the states it allows us to buy TC's when the rate suits us. For example, the current exchange rate is $1.82 to a pound. Makes sense to buy now as 18 months ago it was as low as $1.50! Don't forget that if you do use an ATM or credit card you don't know the exact exchange rate that the bank or CC company is going to levy on that purchase. You can bet that it'll be in their favour though.
We take the majority of our spending money in TC's - and before you get any ideas I'm 6'1, 19st and used to play nose tackle at American football so you ain't nicking it off me! - and then a couple of hundred in $cash. The last time we were in Orlando we didn't use our ATM cards at all and only used the credit card twice; once for buying theme park tickets and once when I went OTT in a Addidas outlet!. However, the good bit was that we still had quite a few TC's left and when we came back to Blighty we changed them at the bank for cash and cleared the credit card bill straight away!