I love the JBL Flip. The JBL Charge is the follow-up, of sorts, to that speaker, and addresses a few of the shortcomings its predecessor had. No more proprietary charging. Much longer battery life. A USB port for charging your various gadgets. It's also louder, and feels just as robust as the already-solid Flip.
The Flip's real selling point, though, is value. I simply don't believe there's a small, portable Bluetooth speaker on the market that makes a better value proposition than the Flip.