I am solidly in the
Mary camp.
Mary is a pristine treasure. I don't find it plain. Rather, I see it as timeless. I wouldn't call it outdated either. It certainly is true that you don't encounter the name like you would have in the past. Other names --
John,
Helen,
Charles,
Louise, I could go on and on -- aren't used like they used to be but they are classic. That's where I would put
Mary.