Are you wanting something for wider shots or portraits? I would not shoot portraits with the 17-55 as the distortion would be unflattering. Portrait length is usually best around 85 so I would recommend the 24-70 but get the 2.8 if able to!
I love working with my 35mm, 50mm and 24-70mm for newborn sessions. The main focus of my business has been Newborns for the last 10 years so I will drop some pearls of wisdom for you. 1. invest in quality not quantity. Avoid cheap items for Amazon or...