Leona sounds gawky to me somehow, I dunno why. And aged. I have always liked
Fiona, although not enough to use because it somehow feels too strong for me - strong the way that strong tea is strong. But
Fiona seems much more current and pretty and appealing than
Leona.
Fiona Marguerite or
Fiona Marian are both good.
I'd probably use Fi or
Fifi if I shortened it affectionately. It does not need an everyday nickname and all of them are awkward if they're not being used by someone very familiar.
For
Leona,
Lee,
Leo, and
Lea all seem to work.
Oni does not, except maybe for a toddler, as it sounds very childish.
Leonie to me is pronounced LAY-o-nee so that does not work. Lee-O-nee doesn't shorten
Leona but could work as an affectionate name.
- mirfak