Never really understood how most people have a set 'am sub/am dom' preference. Reading over other people's responses, I could only imagine picking neutral, because it honestly depends on the situation and changes a lot. I enjoy being a bit sub and I enjoy being a bit dom. Hell, I especially enjoy being a bit more sub at first, only to switch things around half way through or if the pace isn't right. I enjoy giving control away and leaning back to enjoy it, only to turn the tables when they get too used to it. But sometimes I just let them have at it instead, and play along with it.
With my animals though, it doesn't really feel like either in the same way it does with a person. They can't get smug on me and have to be reminded who is really the one in charge. They're just primal, and that's how I enjoy it. No need to be sub or dom when my muscles are locking up so hard I can barely move my body au naturel, and no pretending I'm not getting teary-eyed when being knotted. You can't dom your dog in a manner that they'd understand (At least not safely in my opinion), and they don't exactly understand you being particularly submissive either, so it'd mostly just be imaginary if you tried, unless being mounted is enough to qualify as sub.