Definitely
Annabel. It looks much nicer and I get a better image from it. I would also put the emphasis on the first syllable which I prefer.
Annabelle I pronounce with the emphasis on the last syllable. While
Annabel is a cute little girl with brown hair and rosy cheeks,
Annabelle is a dessert with way too much sugar or that creepy doll from the movies (which is why I think its popularity has gone down like crazy in the last few years).