I pronounce them the same. I like
Isabel better. It looks neater to me. It's not one of my favorite names, probably because it sounds too much like a phrase to me (is a bell), but it's all right.
http://www.behindthename.com/pnl/72895
"Your assumptions are your windows on the world. Scrub them off every once in a while, or the light won't come in.” ~
Isaac Asimov