In MOST cases when you cross show with working lines, you miss out on the best of either line. It's unfortunate, but that tends to be the way it works for all but a small percentage of resulting crosses.
That being said, working ability is defined differently for different people. If what you want 364 days of the year is a pretty GSD that's going to get you compliments wherever you go, knock the socks off your friends, and be a general all around great housemate, then 1 day a year (if that) light up on some weirdo out back of a convenience store who looks like he might have been thinking about going for your wallet... Well a show dog might be exactly what you're looking for. They tend to be calmer, more liveable, a little less challengeing and they're pretty if you're into the whole red/black thing.
On the other hand, if you live in a rough part of town, have to watch your back just walking to your car, and worry that whoever knocks at the door might NOT be the pizza boy... Well, then a show line GSD might not have what it takes to really have your back when the crap hits the fan, so to speak.
My opinion? If you really NEED a working dog, a true working-bred dog (that is need, not want) then you should probably move. Unless you're a police officer, you probably don't NEED a working dog and, the reality is, long-term you're more likely to be happy with a show line. Only because it's less likely to drive you to drink in the first year or two.
This doesn't mean you shouldn't GET a working line if that's truly what you want, but a working line may NOT be what's best for you. I don't think people here think that show dogs aren't worth anything... I do believe that the majority of people who are here are serious working folk and a show line GSD would be useless for THEM. But honestly just about the only USELESS GSD is probably an AKC show line. Don't buy anything that crosses in the Americanized shepherds.
So, ask yourself (or answer here if you like):
1. Which is more important to you MOST of the time? A pretty dog that you can live with, or one that could take out a bad guy (but will probably need lots of work and socialization in order to not take out good guys too)?
2. How much time do you REALISTICALLY have to devote to training? If it's less than 2 to 3 hours, 4 to 5 days a week, you're gonna have trouble with a God honest working line dog.
3. How likely are you REALLY to need a dog who's all grit in a potentially violent situation? Are you more likely to just be frazzled constantly with the dog's extreme drives? Are you more likely to be defending good guys from your overprotective dog than using your working dog to defend you?
Keep in mind that the above are extreme examples. If you raise and train a working line GSD right you will have an AWESOME pet. It just takes WAY more work to get there than a milder line, and if you don't put that work in, the dog is WAY more likely to become a frustration at best and liability at worst.
The key is to be honest with yourself what you truly want and need. Keep in mind that if you live in a generally safe area and are just looking for a deterrent, any GSD will be that.
I have assumed all the way through that you're going for PP not necessarily top level competition. My answer reflects that, so if this isn't the case, please indicate so.
Best of luck!