We love this style of shirt. It's easy to put on because it doesn't have to go over your baby's head and since newborns are swaddled most of the time, they don't need to have a onesie to hold up the diaper.
When my daughter was born, the hospital dressed her in one of these shirts. My husband calls it her little kimono. The sleeves are really long on her, but it's perfect because it prevents her from scratching herself. The side snaps make it easy to put on her, since she doesn't like shirts going over her head.