Natural. My birthstone is diamond and the little imperfections are what make each diamond unique and the flawless ones all the more valuable--because they aren't all just flawless/cookie cutter/etc.
For me personally, I am a natural stone person. I know some people don't care if a stone is natural or lab created. I just prefer to have a natural stone created by nature rather than in a lab. For colored stones I especially like the natural stones because I like seeing the stone's natural characteristics, such as in Emeralds. The created colored stones look too clear, but to each his own.
Nah. It's my friend who recently got engaged. Her fiancé gave her a synthetic diamond which was on sale. Had a court wedding, spent their honeymoon at a hot spring. He is a nice guy but I feel bad for my friend because if it was me I would not marry the guy. But who am I to judge?