Personally, I prefer natural diamonds. Lab grown gemstones, in general, have poor resale value when compared to their natural counterparts. If you're going to go lab grown or natural, you get more of your money's worth through secondhand. Either way, the gemstones should be disclosed to you if they are natural or man-made. I'm biased towards natural diamonds simply because in my family, jewelry is treated as heirloom pieces. Some jewelry pieces in my family date back to to the 1800s.
Shape can make a difference on how sparkly a diamond is. Cushion cuts are more radiant than emerald and tend to be cheaper, but honestly, I think it has more to do with the style of the earring and the personality and/or age of the individual. Emerald cuts tend to be seen with older women because of their higher price tag. On a young person, the emerald cut might look fake or like costume jewelry. I think both cushion and emerald look lovely in a halo setting, but cushion looks more brilliant and "wow" in a halo. You could also opt for a bunch of little stones that are grouped together.
For my own personal collection, I value color and clarity much more than carat and cut. A small diamond that is clear and nearly flawless look so much better to me than a large diamond with some yellowing and flaws. Clear and flawless diamonds, no matter how small, flash beautifully. My suggestion, go into a jewelry store and get a feel for what cut, carat, and setting style you like the most for yourself. From there, you can look to man-made diamonds that are set in the way you prefer.
