I agree with those who said that it's not usually just one or the other. It may be more one than the other, but there are usually several factors involved.

It has also been my experience that the longer depression continues untreated, more and more of the areas in the diagram than von moxie shared become involved.
True. But it may also be the case that you are living with your parents, unemployed, etc., because your depression makes it difficult for you to function.

I have a lot of undesirable things in my life as well. Chronic medical problems, unemployed/on disability, living way below the poverty line, no close relationships, very little contact with parents and siblings, not totally friendless but could use more friends and stronger friendships.

I think it can be helpful to look at the circumstances in your life that you don't like and to make a plan to change them or at least to think about if it's possible. I am only working on small things at the moment, like eating nutritiously, going for walks, and trying to connect with people a little more.

If you are suffering only from what you've called "rational depression", then if you start to make changes in your life to make it more the way you want, I think you'll see your mood start to improve.

Oh - I am never sure what to call the depression that still remains when I'm on antidepressant meds. It's different in nature from unmedicated depression. I suppose it's just a milder version of my depression.

I feel like I haven't answered your question at all. I suppose I just tend to try to find some meds that work fairly well, try to keep my life habits like diet, exercise, and sleep healthy, see where I am at that point then and evaluate what I'm capable of doing to improve my life.