titanium ring in jewelry is the most popular of all gemstones. The price of it and rarity is carefully monitored by the major diamond cartels. As a result the price of diamond wedding ring in jewelry is pretty well standardized to size and quality of the stone.
While the weight of a diamond earrings is important, it doesnt necessarily provide the "perceived size" of a diamond wedding ring. A shallow cut diamond will have a greater diameter, and will therefore look larger.
The most popular wholesale diamonds shape have been the round brilliant because people believed it to be an "ideal cut" that displayed the most brilliance and sparkle in diamond wedding ring.