I adore
Ronit! It's on my MN favorite list and as soon as I find the perfect FN, I'll use it! I like
Roni, but it's too close to Rice-a-Roni (the San
Francisco treat!) and most Americans would associate it with that. I don't know where you live, but that's something to bear in mind. Ronia is pretty; I prefer Roniya because it emphasizes the last syllable (which would be the correct pronunciation). My favorite of the three is
Ronit.