Of these three I find it really difficult to decide which I experience. I'm not sure that I have truly experienced joy at all. I think that the closest I have come is travelling with my husband & walking in wonderful landscapes. What is joy? Supposedly it is great pleasure & happiness. A deep, internal sense of well being & contentment, independent of external circumstances, which lasts longer than fleeting happiness. It is rooted in an authentic life aligned with one's values, meaningful connections, and a profound inner sense of purpose or fulfillment, even in the face of suffering.
That's a lot to ask of life. The obvious response to the question "when did you experience real joy", is the birth of a child or ones wedding day. For me, for very different reasons neither were joyous.
Then there is happiness - a state of mind characterized by positive emotions, a sense of purpose, and a feeling of fulfillment, deep pleasure. Well, yes. I have felt those things. It has usually been relatively fleetingly though. I always mistrust people who seem to be overly happy with their life. In my experience life is a bumpy road, full of surprises & challenges. You have to grab happiness when it happens, because you always have to deal with sorrow & heartache too. I don't think that it is possible, in this world, to feel happy all the time.
So that leaves me with contentment - being satisfied with ones life & circumstances. A sense of inner peace with what you have without constantly wanting more. A lasting feeling of fulfillment that is distinct from fleeting happiness, an appreciation for the present and a sense of completeness. I can live with that & be immensely grateful for it.
The main point of life, as I see it, is to try to do no harm. We all have an ego, a sense of our self esteem & self importance. Self esteem is important, we need to value ourseves. Self importance can be the route to all sorts of problems. Maybe if we thought of ourselves as a grain of sand we would get some perspective of our real importance & be more content with what we have.