Wow, I don't know how many times I've said this over and over in the two Pistons threads, but let me just clarify this for anyone who is looking to buy a pair of Pistons or already has one -- they all sound the same.
The 2.0 version is the original Pistons, that's for sure.
The 2.1 version was an unannounced update to the Pistons with some slight changes to the accessories and the Pistons themselves. Because of these slight changes, there is a chance that one will receive the 2.0 Pistons in a 2.1 box and vice-versa. Like I said, the 2.1 and 2.0 sound exactly the same.
The iF Edition is a limited edition run sold to celebrate the Pistons receiving the iF Product Design Award earlier this year. They come in a more silvery tint than both the 2.0 and 2.1, and have an iF shirt clip, pouch, and box. Though some say that they sound better than the 2.x line, rest assured, they sound the same.