My favorites are [name_f]Elizabeth[/name_f] and [name_f]Isabel[/name_f]/[name_f]Isobel[/name_f], personally not fond of the [name_f]Isabelle[/name_f] spelling.
I like [name_f]Elizabeth[/name_f], but I’m biased because I had an [name_f]Elizabeth[/name_f] in [name_u]November[/name_u].
[name_f]Elizabeth[/name_f] is a classic name but not overused and it has a ton of nickname possibilities. (My daughter is nicknamed [name_f]Libby[/name_f]).
If you like the nickname [name_f]Ellie[/name_f], you could consider [name_f]Eleanor[/name_f] as well.
[name_f]Isabelle[/name_f] is a wonderful name, but too popular for me – there are little Belles and Bellas everywhere where I live.