Purely physically speaking, and gram for gram? Injected. It's all about how much of it is in your blood stream and for how long, and injection is a much more efficient vector. However, someone snorting or smoking may do more, or fool themselves into thinking that as long as they're not shooting up, they're not really "hardcore" yet. Done more than ten or fifteen times without a break they'll damn sure be hardcore enough to go through a full blown opiate withdrawl when they stop.
This is not the place to get information on drugs.
This is:
http://www.erowid.org/