I like them all
Annabel is my favorite (though only this spelling, it looks the most balanced and pretty, also it takes the word bell off it's visual look)
I prefer
Isabella over
Isabelle, and I really like Mirabel (this spelling)though I feel where
Annabel and Isabelle/a are free and don't feel like it's tied to one certain language, Mirabel still feels really authentic french. Actually I'm starting to like Mirabel more and more...I can't decide if I like Mirabel or
Annabel more...