Truth can only be known by the arahants, I have faith in that… so attaining Nibbana is my primary goal.
References :

Many people have offered great responses to your question. I would just like to add a little something.

I believe that each person should read the teachings and gather whatever it is that they experience. For instance, if from your experience it is beneficial to see the 6 realms as literal – if this helps your practice – then by all means should see it as literal. If it is beneficial to see it as purely metaphorical, again, use this to help your practice.

Remember the Buddha said to come to your own conclusions. It’s more important to relate these teachings to your own experience than to believe the words of anyone else, at least in this regard (it would not be beneficial to create your own dharma).

I hope this made some sense. Take care.
References :

The metaphorical explanation serves very well in day to day life, and I’m sure you already recognize that, since you made the connection between hungry ghosts and greed.

There’s another aspect that’s really disadvantageous too, if you really reflect on it. It’s the heavenly realms. If you look at the heavenly realms metaphorically, then these are the people who are born really good-looking, have long life, good health, great intelligence, wit, wisdom, the movers and shakers. We like to think they are much better off than we are, right?

Well, I tend not to get sick. I have very good health. Just recently, I started having problems sleeping. No known reason. I just stopped sleeping. For about two months this happened. It was one of the most painful things I’d ever experienced. I don’t get infections. I don’t get colds, flus, pneumonia..things like that. I’ve never had a broken bone (and I’m a rough player). But that was brutal. I realized that I didn’t really understand suffering. I didn’t get the First Noble Truth.

I was sitting in a very pleasant place all that time (metaphorically speaking), and I didn’t understand illness and injury. I still don’t. I just got a small taste of it. Just enough to tell me that I’m getting older. I can’t keep wasting time. Just enough to tell me that there is suffering…even for those of us who don’t really get sick.

Even metaphorically, the six realms present opportunities for all of us to be free from samsara. It’s just that the easiest one is the human realm, where you have some pleasure and some pain.

But I think they exist literally, too.
References :
Theravada Buddhist