You could narrow down your decision with a bit of information, if you have it. Does your stepson prefer the Light or Dark side? What's his favorite color? Does he have large or small hands?
I don't know if any of that is available to you or if it would even help, but it's a start. However, I can assure you that ANY saber you get will be amazing and your stepson will be in awe the first time he turns it on and hears that sound and sees that light! Nothing ever compares to it.