For a baby to show a preference for a specific person is not only normal, but an essential part of their development. Babies need to form strong attachments to their caregivers for their emotional, social, and physical wellbeing. Usually, but not always, the "chosen one" is the baby's mother. Biologically speaking, it makes perfect sense, but as a mom it's a pretty awesome perk to be the person your baby fancies most. If you need some reassurance (and what new mom doesn't), look for these ways your baby is trying to say that you're their favorite.
At 3 years old, my baby girl isn't a baby anymore, but I remember those early days with tremendous fondness. As someone who suffers from depression, anxiety, and obsessive compulsive disorder, I worried that I wouldn't bond with her, at least at first. In my case, however, I found that her need for me combined with her clear partiality really helped cement our connection. I had my moments when I was overwhelmed, but having that tiny human being show me in her own way that "hey, mom, I love you best" was enough to keep me going.
It's pretty great to have a preschooler who can employ words to express their love for you, but in the meantime, you can enjoy these sweet nonverbal ways that your baby is assuring you that you're their person: