I can also share my experiences...I've always wanted to breed GSD's. Over ten years later I still have not bred a litter.
My first GSD turned out overly sharp and very soft. No good for breeding.
My second GSD (Djenga) had/has a fabulous temperament and nice structure, unfortunately she was diagnosed with HD as a young dog.
Then I got Madina, as a 2 year old. I should have tested her more than I did - but I took the seller's word. If I would have tested her, I would have realized she couldn't be titled. Once I started asking her to do obedience, she completely shut down. I think she had very harsh training before I got her and she didn't have the temperament to be able to bounce back from that. So she was spayed.
Then came Kessy, who I got as a puppy. She has turned out better than I could have dreamed. Great health, fantastic working dog, but I was never able to get her pregnant. We tried several times, with different males, did progesterone, thyroid tests, etc...we did everything we could. I am still heartbroken.
Now I have Kira - I was pretty much ready to throw in the towel after Kessy, but it just worked out perfectly that I could take Kira and title her. I held my breath a little til her teeth came in normally, and then until we had her hips/elbows checked out...they were just done yesterday, but they look great.
Plus she's working out really nicely as a tending dog - and she's gorgeous - so maybe things have finally worked out for me.
With my terriers - I took a gamble on my male (Gizmo), I found his breeder online and had no connections in the terrier world at the time - but he has the most fabulous temperament and great health. I didn't get him intending to breed, but he is so wonderful that it's led to my getting a female.
My female came from one of the top breeders in the country. She's co-owned til she has a litter, and is also fabulous
They've gotten me hooked on terriers!
I probably could have saved myself a lot of heartache if I'd bought PROVEN adult GSD's from the start. But I really enjoy raising dogs from puppyhood, and starting with a blank slate.
I guess this doesn't exactly apply to the debate of buying a puppy vs. rescuing a dog since I'm looking at things from a breeder's perspective. But that's been my journey...LOL