I've never been to a flea market, but I love thrift stores. We have some great ones around here, all the rich people wear something once and then give it to the thrift store. I just got the cutest little Calvin Klein grey silk wrap dress at the thrift store - cost me $10.
I also collect vintage clothes and hats, so I usually have a ball at thrift stores. Some rich old lady will die and her family will unload all her stuff on a thrift store - thats when I come in and clean up. I've gotten some amazing pieces this way.
What exactly is a flea market? Like a big yardsale? I don't like yard sales as much as I like thrift stores, because I find you have to look through a whole lot more junk to find a bargain. In a thrift store, they won't take the junk.