No, I don’t think you can play favorites or have a favorite and be a good parent. I relate to my kids differently because they are different people, it only makes sense. But to love one more than the other means I’d have to pick one to love less, which makes me sick. No way.
I agree that playing favorites–persistently being kinder/more supportive/more generous/more approving of one child over the others–is crap and poisons a family. But treating kids differently is not the same as playing favorites.
My oldest sister is a mess, and has been since puberty: drug and alcohol and bad men and car wrecks and basically a never ending sad country song. I have no doubt that at the end of the road, if the ledgers were tallied, she will have ended up with a disproportionate share of my parent’s time, resources, and energy. But I never felt like they preferred her. Hell, I knew damn well that a lot of the time they were/are frustrated to tears by her. She’s just needed more than the rest of us, and my parents were always big on giving us all what we needed when we needed it.
On the other hand, my mom has a brother with sort of the same problems, but in that case my grandmother indulged him, while being pretty tiger-mom on the rest of her kids. It’s not the time/energy/money difference that has created lingering resentment, it’s the sense that her love for that one was unconditional, and everyone else had to earn it.