I like
Lea because it's different, and I like
Leigh and
Leah too. then again it's just a pretty name all the way around. There is one more variation for
Rebecca, and it's Rebekkah, but then again it's really not that different.
Rebecca is a pretty name, so I like it all the way around.
Alannah is beautiful too, I'd go with Alawna for a different spelling but either way you spell it it's a unique name.