Congratulations! All good advice so far. I'd reiterate that it really depends on how your going to shoot. From my experience, most of my shots came from when I was alone with the baby, which means you need to be in arms reach. babies are like cheap tripods, they fall down, always. So while the longer lens will be better technically in a portrait sense, really they put you too far away to be useful ...."if" ....you're shooting alone. Next is the lighting conditions, assuming most shots will be in the kitchen, living, or baby's room. how is the lighting in these rooms? How big are these rooms? Will you be right on top of the baby? answer those questions and the right lens may rise to the top as I think it would be different for everyone.