Is it OK to have favourites?
I can't tell you if it is right or wrong, and it's probably the latter, but I will tell you how I feel sometimes.
There are some days when one child is just doing everything right. Saying the right things, being polite, helping out and just being all grown-up and mature. And the other two might be fighting, irritating each other and us. You get the picture.
On such a day, it is obviously easy to pick out a favourite. And as human nature goes, I do. But it's probably different every day so I would say that if you average it all out, really every one of them is a favourite.
Also, I try to spend some quality time with each one of them on separate occasions. It might not be a full day outing and might just end up being a short 15 minute walk around a store looking at stuff. For that little period of time, that child becomes my favourite and I try to devote my energy and attention to him or her.
So there.