The best calves are the ones who use social media to congratulate themselves for having specific aspirations or ideas the moment they pop into their heads; because the unparalleled good feeling this form of masturbation brings ironically disincentivizes them from taking the necessary steps to realize the thing. Once they become addicted to farming reward hormones in this manner, they become entrenched within a rut inevitably leading to the mature cow stage of refusing to accept that their lucky break isn't coming. To me, this is the best cow; because they're trained to milk themselves through coping with existential frustrations publicly.
Edit: Also, being fat.