Personally, I think you should decide what you want out of your dog and that should make your mind up for you. As has already been mentioned, both working and show line GSD's need a lot of exercise, the difference being a working line will not stop before you.
I recently started attending a local schutzhund club, because my dog had so much drive, and she loves it. I never planned for her to be a working dog, she has both show and working in her pedigree (I wanted diversity for the health benefits), I just wanted an intelligent companion, that I could train well and would be a great pet, but as she is so suited to schutzhund, i thought I owed it to her to do it.
If you are happy to adapt to the needs of your dog, and are prepared for anything, getting either dog would be fine. If you are prepared to give you dog plenty of exercise, but NOT happy to spend upto 15 hours per week working your dog, then a working line might not be best for you.
Maya, GSD Bitch, Born 30/08/2012..... complete lapdog.