If I could offer only one piece of advice it would be this: Learn as much as you can about 4Cs before you go shopping.

For uninitiated, that's cut, color, clarity and carat weight. And I like to add one more - common sense.

Choosing perfect diamond (and there's no such thing as "perfect" diamond, although a few have come close) is as much a matter of personal taste as it is a matter of diamond's characteristics.

Some couples are willing to forego quality for size, others prefer brilliance of a flawless blue-white diamond over a larger stone with less clarity.

You be judge - but not until you're clear about those characteristics I mentioned. I suggest you read our Diamond Buying Guide, or go to one of quality online jewelers such as www.bluenile.com or www.mondera.com.

Talk to any jeweler and they'll all give you a different opinion as to what they believe is most important quality of a diamond.

According to Mayer Herz, Vice President of Diamond Acquisition at Mondera.com, "Cut is most important consideration if you're on a budget. You can make up for low color and clarity if stone is well cut."

However, Joseph Schlussel, Publisher of Diamond Registry Bulletin, says "I personally believe that color is most important thing. Most people who go into a store today, they are told about cut. But I look at what you can see with a naked eye. I would put cut last, because most people can't see it."

According to Celeste Ohrens, from New York Diamond Traders, "In six months following J.Lo's engagement to Ben Affleck, we sold more pink diamonds than we'd sold in previous six years!"

And despite fact that THAT engagement ring has been replaced with another equally stunning jewel, copies of J.Lo's six-carat pink diamond are still selling well at many Internet jewelers.

When Marilyn Monroe breathlessly purred "Diamonds are a Girl's Best Friend" (as if we didn't already know!), I have no doubt women everywhere secretly coveted baubles Ms Monroe wore, but such flamboyant displays of excess would have offended sensibilities of any self-respecting 1950s homemaker.

Not so nowadays. We've come to expect ultimate in quality and quantity, and if that equates to wearing a 3-carat diamond ring similar to that worn by our favorite celebrity, more power to us!

Whether celebrities are seen as arbiters or slaves to all that is considered stylish, engagement rings gracing left hand of such stars as Catherine Zeta-Jones, Madonna and Ashley Judd attest to fact that their choice of ring design is influencing (or is influenced by) current trends.