EBook or electronic book is a digital book that can be read through a computer, tablet, or mobile devices. There are so many eBook format such as EPUB, MOBI, DJAVU, AZW, EXE, PDF. I'd prefer use EPUB cause it's easier and fit to your screen. Futhermore so many devices such as Apple’s iBooks, Barnes & Noble’s Nook, Adobe Digital Editions, and even for Android support epub files. 

Printed books also has some physical format.  Hardcover book, paperback, mass market paperback. For quality and long lasting use, hardcover is the best one, but for price paperback is cheaper. 

In this inforgraphic below I've explained the advantages between eBook and printed book.

There are also pro contras among them. Some eBooks had pirated so we can easily get free ebooks. Good for us cause we are students, we don't have enough money to pay all the books we want. In the other hand, for writer and publishing house is bad. They don't get any profit so in the future they might be closing and couldn't publish any books again.

Some people say we should restrict printed books, cause to print a book they use a paper from tree. So if we want to save the ecology we shouldn't use the paper. The more we buy the printed book the more they cut down the tree. 

So, which is preferred now?