What is your preferred tool for research; e books or hard copies?

Both. If i did not find what i want online I go the libary.

I prefer E.books when I'm conducting  a research  because of their availability ,, however I prefer hard copies when I'm reading novels , or study for an exam.  

Well, for my area Biology and, specially Taxonomy (one of my interests) both are essential as many bibliographies in this area are very old with more than years! However, I always look first at my hard copies, then in the web (for online scientific articles and books), then in the library of the university, where I make a search for hard copies in it or in others libraries. In the last case, I write for those libraries or some researcher who works in the institution that has the bibliography I'm looking for. 

For research, we should make sure that we rely on a valid source of informations and date, in the first place. "e books" is preffered as it saves time & efforts, but as long as you need to dig for details, I might need to print it out for reading.