Both
Annabel and
Annabelle are lovely, I really like them; my preferred spelling being the latter. It's a shame
Annabel left the American chart 4 years ago.
However, my favourite form is
Arabella. It's less common and I adore its pronunciation and the way it looks on paper.
“Dear optimist, pessimist, and realist – while you guys were busy arguing about the glass of wine, I drank it! Sincerely, the opportunist!”
-Lori Greiner