@facelessk My first ACD girl, Lacey, loved all other breeds, as long as they would romp with her. She had a female golden lab best friend for awhile, she and my female pom got along really well, she had a male gsd mix best friend for awhile. We combined households with a female adult pyranees and that dog couldn’t stand Lacey, but Lacey was oblivious. It was a dominance thing, and Lacey was automatically the top dog in any situation, she didn’t even engage in dominant behaviors, she was just the boss. The pyrenees had been used being the boss in the household and was highly irritated by the loss of status. She growled and harrumphed constantly. I don’t even think Lacey was aware, she just blithely went about her business and ignored the pyr entirely.
My current female acd mix puppy, Josie, loves my rat terrier/chihuahua mix. She’s a senior dog though, so has to shut down the acd sometimes for being too rough. Josie is dog shy with other dogs though, we couldn’t get out to socialize her much and we were nearly attacked during an obedience class, which worsened her anxiety. I need to take her to more training classes (with a different company) so that she can get more experience being around other dogs.
All this to say, it depends on the dog!