I’d say that an internet addiction is much worse than a slinking addiction, because the Internet has the potential to destroy your neshama, while smoking only affects your physical body.
Your neshama represents your eternity- if one gets addicted to the wrong stuff, their eternity is affected in a huge way. IMHO, that is a lot worse than having your Olam Hazeh possibly shortened!
It is true, however, that if one smokes, their life might be shortened in which case they will have less time to accumulate Schar…
Whatever, they’re both awful.