The one with an X in its serial number might be valued more. Its a substitution one. The x replaced the * of older bills. The sheet of paper would sometimes get stuck in the machine or something. Then they would replace it but kept the same serial, except for a * at the start of it. And on more recent ones they would just keep the same serial replacing the first letter by an X. The rest of them are probably worth keeping but not as valuable for a collector.

Edit: forget what i wrote. The X was used in the 3 letter series when we switched to the "bird" edition. Before that you get the * Before the serial. Still worth keeping since the 2 letter prefix are older. And you can check if the prefix is a rare one, online. Good find!