I think any breed can be aggressive and the same for being sweet I think handling when young can help though. Only Two of mine have challenged me at least once in their lives but I put them back in their place and then if it happens again then get rehomed or get a trip to the freezer I have a Frizzle Dominique/Cochin, white Plymouth Rock, Crele Cochin, White Silke, 2 Black Langshans. The Crele and the Plymouth both challenged me once each and the are my dominate Roos. My Langshans are the sweetest in my opinion