I think it more important in a self-portraiture to envision who you are now, and your "true self". I think it is a good idea to envision your "best self", and who you wish to be, but there are also boundaries I believe a person should consider when doing so. You do not want to be always envisioning who you wish to be, instead of who you are. Everyone wishes they could be better at something sometimes, or be someone else. However, it is not healthy if a person is consistantly wanting to be someone else, instead of being happy with who they are.
I think using both is also a good idea. That way you have a balance between the two. You are not just staying content with the person you are now because we all can better ourselves in certain ways. At the same time though, we are not always just dreaming about the person we wish to become, because then we are not satisfied with ourselves. I think a balance between the two is the best idea when envisioning.
It also depends on your theme. If you are doing a self-portait of your life now, your idea in mind, should be the person you are now. However, if you are doing something in the future, or a future dream/hope, then it is okay to look beyond you now, and think about who you might be in the future.
