They are both important, however I think to forgive others you must forgive yourself first.
Its like being strong, you cant be there for someone unless you are strong yourself.
However I have to agree that it is unhealthy for anyone to hold this hatred/guilt in.
Others that do not forgive you, obviously think they did nothing wrong and have not forgave themselves. This proves that you are a much better person.
Its like walking away from the argument. If you stay you add fuel to the fire. So if you do not forgive yourself your guilt adds fuel to the fire and leaves a miserable feeling inside.