What Necklace Should I Get My Girlfriend For Valentine’s Day From Tiffany & Co?

My girlfriend told me she always wanted a tiffany;s necklace, and so I got $250 to spend at tiffanys.com. This includes tax and shipping. Shipping costs $15. Basically I have $235 to spend including tax. Here is the problem, I dont know what girls really like. I need suggestions please. All the ones I showed my friend he said they suck. Anyways please leave suggestions.