I'm not having kids because I don't have any interest in devoting eighteen years of my life to taking care of them. That's a level of commitment that I just am not interested in. I'll borrow my sister's and spoil them rotten, instead. Best of both worlds. That said, if I did, I probably wouldn't tell them there's a Santa Claus until I was old enough to see if their personalities would enjoy the myth or not.
Don't get me wrong. I love magic. I'm a 26 year old woman and my room is decorated with unicorns. But not every child is the right fit for the Santa myth.
Personally, as a kid, I didn't like Santa! He didn't creep me out or anything. There was just something about him that seemed wrong to me. It didn't make sense that he did all those houses a night, and how could he eat 12 billion cookies without getting sick? What made reindeer fly? What distinguished the arbitrary difference between good and bad girls and boys? Nobody could provide any satisfactory answers and always seemed annoyed that I was asking the questions. Christmas became frustrating for me as I felt myself constantly being pushed to stop asking questions, which was a part of my personality.
I got more and more resentment for Santa because of how I wasn't allowed to question his authority, until I started running experiments. I tried to see if I could trip Santa up. When I went to sit on his lap at the mall, I asked him for a bunch of stuff I had no interest in. I gave Santa one list and my parents another. When none of the gifts I'd asked Santa for showed up, and all the gifts I'd asked my parents for had, my theory was proven true!
I confronted them about it. I was so mad at them. Why hadn't they just told me? Did they think I was dumb? It was a whole big blowup. I was about five and a half at the time.
I'm not still upset about it, obviously, that would be dumb. It definitely wasn't traumatic. But I never got enjoyment from the Santa myth, and it spoiled a couple Christmases for me. I still wish that my parents had just told me the gifts were from them. I love getting gifts and love my parents, and knowing that my gift was especially picked out for me by someone I love so much was worth a thousand times more for me than getting them from a magical stranger who judged me all year. I'm really glad I found out about Santa so young. I wish I'd found out younger. I wish we could have just skipped the whole dumb thing.
But my sister, oh, my sister. She believed in Santa until she was twelve, and even then clung on desperately for another year hoping she could stay in the magic. She loved Santa Claus, everything about him. She made the cookies almost entirely herself from the time she was seven on. She was devastated when she finally admitted he wasn't real, though she doesn't hold it against anybody either. She'd never change the fact that she believed in him for so long, and I'd never take it away from her.
A baby doesn't understand Santa, so there's no point starting it that young. By the time they're three-ish and able to form real memories and concepts, I think you'd be able to tell who they are. Do they ask a lot of questions? Are they satisfied with simple explanations? Do they point out the inaccuracies of your claims? Or are they more accepting, with a more childishly simple curiousity? Are they gullible? Are they skeptical? Not every child is the same, and one magic spell doesn't fit all.
TL;DR: my point is that Santa is a good fit for some kids and not others. I don't think parents should just assume the right choice is the myth. Wait until your kid is old enough to get it, and for you to get them, and then make a choice based on their personalities. I wish I could have gone without Santa. My sister wishes she could still have him. Children are different sorts of people just like adults.