I've had experience with both German show and working lines. There is a lot of room for individual variation, but IN GENERAL: the working lines seem to have a bit more "edge" to them when they are working. If you watch videos of show dogs doing SchH bitework and then working dogs, you'll notice it.
Some of the working lines can be a bit much for a family to handle. The energy and drive in some working dogs can be intense. They *should* have a good, stable temperament, though. Not to say that show lines are lazy, they have plenty of energy for everyday doggie activities and more.
In Germany, every GSD regardless of bloodline must complete, at a minimum, a SchH1 or herding title in order to get breeding rights. So you could argue that show lines also work. Most males of both bloodlines acheive SchH3. Showline females generally get a SchH1 and then go on to maternity duties, while working line females often go on to SchH3. Both bloodlines must have a show rating as well. Most showline dogs will have a VA (excellent select) or V(excellent) in front of their name. Working line dogs will have G(good), SG(very good), or V(excellent) in front of their name.
The most noticable difference between bloodlines is color. German show lines are almost exclusively black and red saddlebacks. Working lines come in all colors, sable, bicolor, black, and saddleback. Show lines tend to have more angulation in the rear legs, and--to my eye--have a sort of "cookie cutter" appearance when you line them up together. All plush coated black and red saddles, some with a humpbacked appearance when stacked in a show pose. I personally like the look of the working lines, the more moderate angulation, compact solid build, tight cat feet... but that is just one person's opinion.
Just so you don't think I'm TOO biased, I have to add this. A client is bringing his German showline female in for grooming, she's now about 9 months old I believe. I would steal her in a hot second. Lovely bitch, not overdone, sweet temperament, calm and compliant with everything I do to her, takes everything in stride. She is what I'd call the perfect family dog.