OSB and very happy!
HD sells 1/2" OSB for less than five bucks. It is WOOD, cuts easily, and hangs easier than drywall. No taping and mudding.
It is all screwed with drywall screws for down-the-road mods to electrical, etc. Right now, it is still bare, but I intend to paint most of the walls white to reflect light. Some I may cover with TG Poplar since I have several thousand sq ft of it reclaimed.
I can screw, drill, cut, paint, undo, and redo to my hearts content cuz OSB is the cheapest per sq ft that I found and it is sturdy enough to handle most anything I throw at it (sometimes literally).
This above all - To thine own self be true. Wm Shakespear - Hamlet