My mom used to be terrified of GSD and Rottweilers. A GSD attacked her dog when she was walking it one day (I think Mom was maybe 10?) and the dog's ear was torn off.
Then she met my uncle's dog, Duke. A HUGE GSD, he ran up to Mom, jumped up, rested his paws on her shoulders and started panting in her face. I'm not sure what the deal is with Rottweilers, but she's fine with them thanks to the same uncle who had one after Duke died.
I do know that as advertised as labs are for "family dogs," they tend to be facebiters. My dog once nipped someone so hard he drew blood. However, he only does it when someone provokes him. For the most part, he's docile (even more so now - his 12th birthday was yesterday!).
I'm very partial to dogs that have a bad reputation because these dogs are usually very smart, but people only see the bad side thanks to the media.