Do you need to play the first Chaos Rings to understand Chaos Rings Omega or Chaos Rings 2. Have heard that these games are great and wouldn't mind checking out at least one of them while they are on sale
No. Chaos Rings actually happens after Chaos Rings Omega, and Chaos Rings 2 is set in another Universe, so it doesn't have much to do with the other games. You don't need to play Omega to understand Chaos Rings either.
You can't go wrong with any of the three games, but yeah, probably Chaos Rings 2, although I found the story to be better in Omega.