My two favorites are Zig Writers (double-ended, two different tips) and Pigma Micron. Both are acid-free and permanent. They don't fade or run or smear. I own a variety of colors and sizes and use them all. If you are just wanting one to do this baby book, then choose your favorite color. You can purchase in sets or individually. I tend to write big, so I go for the smallest sizes for writing captions and details. I use the thicker sizes for page titles and random doodling.
"Kind words can be short and easy to speak, but their echoes are truly endless." - Mother Teresa