Rey to me is definitely Han Solo's Daughter. It makes sense, It would be weird if she was Luke's and there where so many moments in the film that hint at this being true.
For instance the millennium falcon, she knows everything about it she is a fantastic pilot and engineer just like Han. Rey and Han even say the same phrases at the same time at one point and there is an instant bond between Rey, Han, Chewie and Leia. I think Leia had twins and one was possibly hidden from her and Han by Luke so he could train Ben without distraction, maybe Obi Wan told him to make that decision wisely and he did, and now Rey is restoring the balance in the force. Ben and Rey have to be siblings it would make a great moment for episode 8, can you imagine Ben or now fully turned cyborg Kylo Ren just like grandad says;
"Come with me to the dark side Rey, as brother and sister we can rule the galaxy and fulfill are Grandfarther's dream and overcome Snoke together".
That would be awesome in my opinion and would mirror the past somewhat. Alternatively she is Luke's daughter and all the hints where misguidence from JJ Abrams and there is more to Luke's background than we think ...... Maybe, I don't know, but that takes the sibling rivelrey out of the film and makes it less intense between the two main characters, Rey and Kylo Ren. Brother killed Dad and now Sister is gonna kick his ass and in my opinion cousin rivelrey just is not the same.
What do you think ?