Between
Ella and
Ellen, I'd take
Ella.
Ellen has never really appealed to me, it sounds dated and needs some time before it is ready for a come back.
Elle and
Ellie are nice nns, I do not like them as full names.
Eleanor (
Elinor!),
Ella,
Ellie,
Elaine,
Elle,
Ellen
Top 50 or so is still popular enough that it would be widely known to people, which could cause it to sound dated without being over used.