Based on my experience there are two: clitoral orgasm and G-spot/vaginal one. And to spice it up there's the blended one. I don't know if I could ever orgasm from nipples alone, but I do feel like I'm getting close sometimes if the Moon is right...
However, for me a true orgasm is the vaginal one. I enjoy the vaginal ones more than anything else, they come without clitoral stimulation easily enough to me within just a few minutes from penetration in the right position (and the right level of arousal of course). For me it's boring and comfy old missionary (with it's variants) or cowgirl that works best and never ever came through doggy for example. There is just one special spot on the front of my vagina's wall - and interestingly enough the penis is that spot's preferite toy. My husband's fingers work well too, but with toys it's much harder to replicate the right stimulation. Thrusting also works better for me, instead of the famous "come hither" motion or poking it.
I know most will not agree with me, but I am a firm believer that vaginal orgasms are the ones we were intended by nature to have. That is why I also believe that all women are capable of having them. Mind you, I have passed eight out of my sexually active years without one, so I'm not speaking as someone who's always had them easily.
It is very difficult to explain how it feels, but there is a huge difference between clitoral and vaginal orgasm. This is going to sound like a very stupid analogy, but bear with me. Imagine a needlle puntcuring (superficially) one nerve ending on the outside of your nose. You get a temporary sharp pain that might travel around on your nose a little bit, but it will fade away quickly anyway (depending on your skin's sensibility). That is what a clitoral orgasm is for me: superficial and short-lived. An external sensation ON my body.
Now imagine the same nerve ending being punctured from the inside of your nose. (Just think of a sneeze to help you imagine what it must feel like having that needle inside to stimulate it.) The perception of the puncture will feel like a burst from the inside. It will travel further, feel more intense, last way longer. You might also have psychosomatic aftershocks of that disturbance in the nose long after the needle left your orifice. That is how I feel my vaginal orgasms: more subtle, yet more intense, longer lasting (in time and in memory), and something that travels INSIDE my body starting from my vagina (depending on the intensity, the sensation can physically travel up to my neck and down to my knees).
I'm not sure I made a good analogy, but it's real hard explaining to someone who never experienced one. I can only say what I was told before I got my first vaginal orgasm: "you'll recognise it when you've had it".
Having said that, combine the depth of a vaginal orgasm with the strenght of a clitoral one, and blended orgasms can literally be mindblowing!