Neither are to my personal taste, but if I had to pick, I think Audrey.
Mabel either makes me think of cows and it's too close to label. Yeah, weird reasons, I know! It does have some nice shortening though, like May or Belle.
Audrey makes me think of Coronation Street! But I think it's a nicer sound than Mabel, and has nice connotations like Audrey Hepburn.