Isobel is a completely different name to me, as I pronounce it EE-so-bel. I like it a lot pronounced that way.
Isabell is the
German spelling and very common here, but I dislike it. It looks very unbalanced to me.
I like
Isabel and
Isabelle equally. They both look very nice. I'm not sure which one I'd choose, I think today it would be
Isabelle.
I know heaps of Isabels which is why I'm not very fond of the name. I went to school with an impolite, silly and stupid girl named
Isabel and later with a stuck up girl named
Isabell. There was a bitchy
Isabel in my dance class.
Now at my university I have classes with three girls named
Isabell and
Isabel. They are nice. Still I'm not a fan of the name. If I had to use it I'd go with
Isabelle (because I don't know anyone with the spelling and it reminds me of a character in my books for French lesson plus it looks nice) and I'd call her
Belle (most girls named Isabel/l I know go by
Isa or
Isi).