Either, I use both. Most new titles I read are via a Kindle Fire (I steal one from the kids). But I still like to pull books off the shelf I have read many times, and in that case I read hard-copy.
Growing up, I probably read nearly every Louis L'Amour book in existence. My Dad was big into Westerns, and those books played a big role in shaping how I look at the world. Just recently, I was thinking that my 11 year old boy might enjoy some of those books. So, I borrowed about a dozen from my Dad, and I am trying to get my kid into them. He is most of the way through his first one, but I have read about 6 or 7, already (or re-read, I should say).
They are super quick (usually 170 pages of paperback), and they are very black and white: the good guy is completely virtuous, the bad guy is bad to the core, and the hero always wins and gets the girl. They can be a fun read, and I have enjoyed re-visiting them. But, they are essentially reading junk food, so I should probably consume them lightly.