I prefer it Madeleine (the French spelling, pron. more like Mad-e-lehn)
Actually (and this makes me feel a bit guilty but it's true) my most preferred form of the name is Madlen.
Mad-eh-line with line as in Caroline seems unnatural to me, since I have never heard anyone pronounce it like that. It seems like she'd have to train everyone she met. Which wouldn't be a big deal.
I don't think the rhyme would matter since Caroline is a middle.
- chazda