Honestly, the best dogs I've ever had have been mixed breeds (mostly pit/American bully mixes). I've fostered over 16 of them this year for the local shelter, and let me tell you I only had a couple that would slightly misbehave. They really have been the most LOYAL and friendly dogs I've ever come across. They really were Velcro dogs...aha I would have to run to the bathroom and shut the door so they wouldn't follow me in. And when I came out they would be right there sitting in front of the door.
When I first started fostering the pittie mixes I thought for sure they were all going to kill my cats lol...but NOPE. I haven't had one try to do anything more than play with them. They have all been extremely smart as well. Just excellent, excellent dogs.
These were mostly the "southern" type pit mixes, so they had a narrower build than the short and stocky ones. Most of my fosters had a great energy level. Not too high strung but not too lazy either. The last one I just adopted out would run alongside my bike forever...never tired. But at the same time, she wasn't terrorizing my house. Whatever I did, she did. So if I wanted to watch a movie she would lay right beside me.
I had an Australian Kelpie from the shelter once and he was hell on wheels lol...tried to kill my cats, chewed everything in the house, peed everywhere. He actually had to be put down because of his aggression toward people. I also had a Australian cattle dog mix who was wonderful...great Frisbee dog...and lastly I had a purebred golden retriever foster whom I trained to be a service dog. He was quite literally the laziest dog I've ever seen. Just laid on the couch. All the time. Sweetest dog, but very boring...
Honestly, I say get a mutt from the shelter. It's going to be a hell of a lot cheaper, and I think (personally) they turn out to be the best dogs.