In terms of proportions and the "what you look like from an objective point of view," it's the camera.
Mirrors show you the opposite arrangement of your features, flipped (as one would imagine) to a 'mirror image.' Because the sides of your face aren't symmetrical, this creates a familiarity with a specific arrangement and proportion of features. This is not however, what other people see when they look at you.
A camera shows your face in the appropriate arrangement, which is opposite what you're used to seeing in mirrors. This explains why people who aren't constantly looking at photos of themselves are generally a bit unhappy (or at least "meh") about photos of themselves, feeling it doesn't look like them.
There are other factors, too. Photos are more likely to bit lit in a favorable way, while very few bathrooms have a good mix of key, fill, and back lights in relation to the mirror. So even the textural advantage of mirrors can be misleading.