Honestly, I don't know. I've bought two diamonds, 30 years ago and 10 years ago.
The first one was my wife's "first" engagement ring. I bought it because (and this goes to show you how these decisions are made sometimes) it weighed in at EXACTLY 1.000 carats, had 'D' color and was flawless except for a single tiny feather that could only be seen under magnification. It cost me $4k.
20 years later, it turned up lost. My wife 'bout had a nervous breakdown over it. Since we were coming up on our 20th anniversary and our circumstance were conducive, I bought her another diamond to mark the occasion. This one is just shy of 2 1/4 carats, F color and no discernible flaws. It cost me $12.5k from a local jeweler that I have a good relationship with.
BTW - the 1st diamond turned up 6 months later. Found it on the kitchen counter, under a shelf. There's no way it could have been there the whole time. While we maintain the "mystery", I also know that it's not uncommon for engagement stones to go missing from time to time, only to be found after they've been replaced by something bigger.
She had the older one made into a pendant, wears it every day and it's gorgeous. That's the thing about a really good diamond - they're heirloom pieces.