When my husband proposed, he picked out a diamond and put it in a plain setting. After I said yes, he took me back to the shop to pick out the setting/ring. He said that, if I didn't find anything I liked, he could return everything and go elsewhere, but I told him, "if I can't find anything acceptable here, you need to throw me back."
I wouldn't care what kind of diamond it was. I'm practical and would probably choose the lab grown one if it looks nice and is cheaper, but hopefully you know how your girl thinks. Some girls care about brand and doing it the old fashioned way. Some girls are more practical.
Does she care about name brand stuff? If so, she might prefer the natural, dug from the ground diamond. Is she practical and likes a good deal on quality? She might prefer the lab grown diamond.
I can't say that I have ever compared the two. Chemically they should be the same, so if you can get more clarity, purity, and sparkle for the money, I'd go the lab grown.
That's what I'm thinking. Good lab grown diamonds are more perfect. You can get better clarity rating and more carat weight for less money.
A friend of hers got his fiance a $10k ring and she told me don't you dare finance a $10k ring for me like he did. She's more practical than that.