Susannah is classic, timeless, and uncommon. It would also be a tribute to my husband's grandma, Susan. We would use the nickname Sanna/Zanna instead of Susie... Savannah is more modern, trendy, and pretty common (at least where I'm at in the US). We would nickname her Vanna if we used this name. Both mine and my husband's families use nicknames, so we'd like to get one established already before they do. (I've gone by an uncommon nickname my entire life and I've never had someone call me anything different after I've introduced myself, so I'm not worried about people calling her the wrong nickname).