A mirror will be the reflection of your all bathroom. It should be large, aesthetic and it should fit your sink’s style. A larger mirror will show your bathroom bigger than it is.
It is very important to catch the harmony between the sink and mirror. Match your mirrors over a pair of pedestal sinks. This would create a symmetry. A curved mirror without any frame can be good option for a master bathroom. But if you are male living alone in your flat, don’t forget that this style has a side of femininity. With a framed mirror, your bathroom will look more finished. If you want to transform you unframed mirror into a framed one, cut molding from your local hardware store to fit your mirror, paint it and attach it to your mirror with construction adhesive. Use white, because imperfections in the corners can be caulked and painted for a seamless look.
Here is a trick. Make sure that the mirror is 5 feet off the floor. Do you know why? Because average line of sight of human being is 5 feet, so it is a good rule of thumb and a good trick.