In my language, definitely strong, elegant, somehow Medieval/Renaissance feel, romantic Perla (which means pearl) 
Agata is a nice name in my language, too. It is the name of a gemstone.
Ambra in my country means amber and I like the sound kinda but I wouldn’t use it because it feels too modern.
[name_u]Love[/name_u] gemestone names picking my only one favourite is ridiculously hard!!!
From your list I’d go with [name_f]Opal[/name_f], as I love the stone and its not terribly popular as a name.
I personally would use [name_f]Emerald[/name_f] in a heartbeat for my next daughter but if my partner didn’t object then I’d use my absolute favourite gem name: [name_u]Lazuli[/name_u].
Choosing between [name_u]Ruby[/name_u] and [name_f]Pearl[/name_f] is painful, but I think [name_f]Pearl[/name_f] just has it - I’ve met a lot of Rubys, and there’s not an accessory prettier than a pearl necklace. I like [name_f]Opal[/name_f], but as a middle rather than a first.
[name_f]Esmeralda[/name_f] is my favorite
From the list I’d pick [name_u]Jade[/name_u] or [name_u]Ruby[/name_u]
1 : [name_f]Sapphire[/name_f] 
2 : [name_u]Jade[/name_u] 
[name_u]Jade[/name_u]
[name_f]Sapphire[/name_f]
[name_u]Ruby[/name_u]! 
I like [name_f]Amethyst[/name_f] the best. It sounds so beautiful! [name_f]My[/name_f] favourite out of your list is [name_u]Ruby[/name_u] for the same reason.
[name_f]Jewel[/name_f] is my favorite!! 
Of yours, I think [name_f]Opal[/name_f]! [name_u]Love[/name_u] [name_f]Pearl[/name_f] too, though.
[name_f]Gemma[/name_f]
[name_u]Jade[/name_u] from your list.
[name_f]Sapphira[/name_f], hands down. (well that, assuming a variant is allowed. If not my second choice is Pearl).
[name_f]Pearl[/name_f], because of the versatility and vintage charm.
[name_u]Jade[/name_u] is one of my all time faves