How do I choose the best dress for a formal event?

Recently, I had to choose a dress for a formal event and I can truthfully say that I didn't realize how many of the details would come into play until I began looking.I even leisurely walked into the local shops and checked out some pieces from alibaba and other marketplaces ***just to see the styles and prices - at first, it was a bit of a shock. The things that helped me were to focus on the type of event, the fabric, and how comfortable I would feel wearing it for long periods of time. I began to notice things such as the stitching, how colors looked in various lighting conditions, whether or not the design was too flashy or just right. Well realization hit me that it’s not the trend but rather on how comfortable you are in your outfit. I'm wondering what you normally do, go for simplicity, go for designer or go for something that is still stylish and doesn't cost as much? I'd love to hear what helps you all, too.