A selfie is a casual picture that one takes of oneself on a smartphone. The intent of a selfie is usually to post on social media. A selfie has recently become very important for social media purposes, as a way to express yourself and to show others what your're doing. A self portrait is a picture that you take of yourself on a professional camera. The self portrait is normally taken more seriously than a selfie, because there's more time and thought put into taking the photo.
A selfie is normally taken at arms reach, or taken of oneself in the mirror. A selfie is taken spontaneously, and as opposed to a self portrait, not much thought is taken into consideration in preparation for taken the picture. A self portrait is normally taken on a professional camera that is put on a tripod. A self portrait requires a lot of thought about the face expression, background, and clothes that are worn.
I prefer a selfie because I think that it is more relaxed and more usable for everyday pictures of oneself.
I don't think that either one is more valuable than the other one. This is because they're each used for different reasons. So, the selfie is more valuable for the purpose that it's used for, while the self portrait would be more valuable for it's purpose, as opposed to a selfie in that situation.