Speaking in rough generalizations, yes a working line dog is likely to have more aggression than a show line dog. That said, you can find a safe dog in any of the lines. I will say this, though. Plan to do lots of training. These dogs need structure, and their brains need to be worked. They also need quite a bit of physical exercise.
What I would do in your shoes would be go to clubs in your area and see dogs of different line types doing various things with their ownders/handlers. Local kennel clubs, your local GSD club, schutzhund clubs. It doesn’t matter if you have no interest in pursuing those venues once you have your dog. Observe lots of dogs. Talk to owners. Find out what their dogs are like at home and out in public. Ask if they are good with kids. Ask if they are reactive. Ask what their health has been like. Ask if they have a good off switch in the home. Ask what the experience with the breeder has been like. Find your breeder by seeing dogs you like, not simply by recommendations on the internet.
I have not owned either a WGSL or an ASL dog, but I have met nice, stable representatives of both line types. Both line types would be a visual deterrent, and both would likely alert you to someone at your home. I have two working line dogs. One would be an absolute nightmare for someone who wanted a kid friendly, take anywhere kind of dog. My girl could live as an active pet as long as someone was willing to provide an outlet for her, mentally and physically. Both have more aggression when pushed than show lines I have seen. Don’t rush to get a puppy. Do your due diligence with finding an honest breeder who produces healthy, stable dogs.
All of this is excellent insight to keep in mind.
I'd like to chime in from the perspective of owning a show line dog (75% ASL/25% WGSL cross). I think a dog like mine would fit your bill very well,
@khk410, and I don't think she's terribly unusual in that she is safe and stable and would do well with an active family with kids. My city has a lot of dog-friendly businesses, and my dog is a "go all the places, do all the things" dog. She will definitely alert me to any goings-on outside our house (she's trained that this is fine, I go and look out the window and then tell her to stand down), but when we're out in the community, she isn't reactive or quick to decide something is a threat. She's dog-neutral to dog-friendly, and she goes weekly to daycare and to the dog park on a regular basis. I'm not certain how typical the dog-friendliness is, to be honest, but she's been very easy in that regard.
I do want to emphasize that you should not discount the amount of physical and mental exercise required by a show line dog. Mine needs both. She can roll with one or the other if she needs to, but she really does best if she gets one thing from Column A (walk, fetch, dog park, active game) and one from Column B (Nosework, other class, tricks practice, puzzle toy, etc.). She can get pretty demanding about the latter, too; I don't have much luxury to be mentally exhausted at the end of a long day and not spend time with her. And that's fine, I signed up for that, but be aware that an ASL dog is not necessarily going to be your Netflix buddy even if they're lower drive. She's a pretty busy dog between about 6 and 10 or 11 PM, but to be fair to her, I'm getting home around 6 and my husband works from home full time so she has been taught that she needs to be chill during the day and the fun starts when I get home; we pack a lot into those 4-5 hours. Right now we do classes 2 evenings per week, and that seems to work really well for her. Put it this way, we're doing 2 classes per week plus we have 2 full-day Nosework trials and 3 half-day trials coming up in the next two months, and my only worry about her stamina is the weekend we trial all day Saturday and then turn around and do 2 half-day trials back to back on Sunday.
But if you are active and you/your family are able to spend quality time providing both physical and mental outlets for the dog's energy, a show line dog would probably be just as good of a bet. And I don't say that to take away from any working line dogs - I've met WL dogs who are easier to have in the house than my ASL/WGSL dog and who are every bit as stable and safe and fun to own. I have not ruled out owning one myself someday. As GypsyGhost said, you would be able to find a safe, stable dog from within either type, and I would repeat her advice to go out to clubs and meet dogs and owners and breeders, and ask all the questions. This specific type of research is actually not something I did, I gained it piecemeal after I got my dog, and although I'd have ended up with the same breeder had I done it, I would not hesitate to recommend that you try to do it beforehand.
