I think [name_f]Rebecca[/name_f] is the original and it is definitely the more common spelling but I much prefer [name_f]Rebekah[/name_f] 
@findemaxa13: The older spelling is Rebecca, which was used in the Bible since at least the 4th Century A.D. (in the Latin Vulgate translation of the Bible). Centuries later, when the Bible was translated into English in the 1600s: The spelling “[name_f]Rebekah[/name_f]” was used by translators of the Old Testament, while “[name_f]Rebecca[/name_f]” was used by translators of the [name_m]New[/name_m] Testament. However, the ancient name in the Hebrew language is written with entirely different characters… not the alphabet that we know. StripedSocks posted the Hebrew version of the name on the previous page of this thread if you wish to take a look.
@StripedSocks: Thank you for the additional information you posted about the Hebrew source behind [name_f]Susanna[/name_f]. BTW, I like the spelling “[name_f]Susannah[/name_f]” too.
[name_f]Rebekah[/name_f]. I don’t like [name_f]Rebecca[/name_f] it looks odd to me.
Interesting, the Bible translations I have used seem to use the [name_f]Rebekah[/name_f] spelling, so I have always assumed that was the original and [name_f]Rebecca[/name_f] was a modernisation. Looks like I might be wrong.
When I was very young I named one of my dolls [name_f]Rebecka[/name_f], as I thought that’s how it was spelt. I could never work out why that spelling was never used!