I prefer [name_f]Nina[/name_f]! I’m gutted it doesnt suit our last name!
I love love [name_f]Iona[/name_f]! But you can’t go wrong either way, [name_f]Nina[/name_f] is lovely too. 
[name_f]Nina[/name_f] is lovely but [name_f]Iona[/name_f] sounds really cool to me and I love the nickname [name_f]Io[/name_f]. (I’ve never found [name_f]Iona[/name_f] hard to pronounce but I live in [name_m]Britain[/name_m] and it might be a more familiar name here than in other countries?)
[name_f]Nina[/name_f] is my #1 girls’ name, so my opinion here is biased 
[name_f]Iona[/name_f] is beautiful, but I do see people easily misreading the capital I for a lowercase L