From past experience, I would say to stay away from anything American if you are looking for stability. Unfortunately, a stable, healthy AKC shepherd is the exception, not the rule. West German lines tend to make better companions then East and Czech lines. If you go to the United Schutzhund Club of America online, they will point you to reputable breeders as well as clubs. I know you are not interested in schutzhund, but it is a sport that was developed to create the best all around, working and companion dog. A reputable breeder will be able to easily pick a puppy who will be less drivey, but just as stable.
Show lines tend to be harder to deal with because of the emphasis on looks not working ability, but West German Show lines are 100x more stable then american lines. Above all, find a breeder who is not TRYING to sell you a dog. If someone pushes a dog on you, thats because they have to do that to market their dogs. If they are careful to make sure YOU are a good fit, you can bet your boots they will make sure the puppy fits your lifestyle.
Awesome...someone else stating a sweeping generalization and bashing a line.
American lines are fine. There are plenty of stable dogs out there and you just have to know where to look. WL can be just as unstable (and even more so lately due to the sable/WL fad that has hit the pet market). I've seen way more unstable WL in my club's puppy classes than I have American lines...mostly due to people breeding sables with no regard for pedigree.
Anyways...about the cross. I've dealt with a few, the most recent does have bad nerves and gets stressed really quickly. His owner works him in obedience, but once he's reached his threshold she just pulls him out of training and he goes in the car to relax. He isn't reactive, aggressive, or anything bad, just kind of shuts down and doesn't want anything to do with whatever is going on around him. This cross was the first and last that the breeder did though (owner is the breeder) because she was pressured by our club to use a Champion sire. The dam doesn't really have over the top drive either, I would call it lower than average for a working line, and so the dog doesn't have that high of drive either. Remember...genetics doesn't work that you get exactly what the parents had. So it really does depend on both the dam and sire that the breeder is using. If she's had success in the past...she probably knows what she's doing and has had some pretty good puppies.
I'd like more information though...is she using the same dam and sire over and over again (questionable practice as there is no long term goal that way), how far back are the mixes happening (mother/father, grandparents, ect)? There is a lot to look at when evaluating a breeding, and the problem with this one is that there will be "WL experts" and "ASL experts" and neither will agree because they can't really say for sure what will come of the cross.
I should add...I also have dealt with a few good crosses. They were calm, had good nerves, and no where near as drivey as a WL. But this is what the owners and breeder was looking for and they succeeded.