How many comments are there about Tiffany being plain which are from guys? If you hear from ladies point of view, Tiffany is a brand where they will feel proud if someone ask them where the necklace is from. Girls would rather hear it's from Tiffany then from Swarovski. They aren't materialistic, it's just that the branding power is that great.

For example, ask a girl if they want a 1 carat from Selberan or a 0.7 carat from Tiffany, which assuming they are of similar value. Of course some girls don't care. But to many, deep down, they have a preferred brand. Big isn't always better as the saying goes.

Anyway, TS, you know her best. If your options are only those 2, I'd go for Swarovski.

After hooking it, gently run your hands down her back, to her waist and twist her around, look into her eys and say, "beautiful and I'm not referring to the necklace". Brownie points man