Definitely paperback. When I bought physical books, I always waited until they came out in soft cover - that hard cover junk annoyed me to no end.
But ultimately, e-books are win: you can read them on your phone, tablet, ipad, and an e-reader : and when it comes time to pack up and move, it's 1000x lighter. Convenience is win (after all, if you have at least 3 of the above mentioned things; then battery isn't an issue ;o) I /love/ the digital age.