I like
Ellen better. I think
Ella sounds like a nickname... it's sort of light and fluffy, whereas
Ellen has some weight.
I don't know that
Ellen will make a comeback in the near future if it hasn't already.
El- names are popular, and so are -en endings.
I do not like
Elle or
Ellie as full names. I don't even like
Elle as a nickname.
In order of preference (used as full names):
Eleanor,
Ellen,
Ella,
Elaine,
Ellie,
Elle
I like
Ellie quite a bit as a nickname, but not as a full name.