First try on the blush, a little on both your cheeks to give you that flushed and lovely look. Bronzer is to give your face a tan look and therefore can be used when you want a glam effect.
The basic difference between a blush and bronzer is that while blush is just for your cheeks, bronzer is for your entire face, it gives your face a healthy shiny glow, as if it is sun kissed. It is therefore a natural choice for many. The best thing to do is to use a combination of both.