Fast, slow, I just enjoy riding.
When I feel strong, fast is good. Otherwise, or in casual group rides with friends, slow is good.
However when I improved my conditioning by pushing harder than I was comfortable with to get faster, I was also more comfortable on slow rides and enjoyed it more. Being able to ride faster isn't just for the sake of being fast. It's nice to be able to loaf up a climb while chatting with a friend, on the same hills that used to leave me gasping for breath or getting off to walk.