How do i decide between wallpaper and painting?

I have just stripped the liner paper from the walls and ceiling of a room. In some parts of the room there appears to have previously been damp and the previous owners have removed the liner paper and painted directly onto the wall with a thick paint. In other parts of the room the top (skim) layer of the plaster has come off when the wallpaper steamer was used to remove the wallpaper. Should I: (a) hire a plasterer to redo the bits where the plaster has come off and then paint the room, or (b) hire a decorator to liner / wallpaper the entire room (and then paint over) Which is likely to give the best result? Which is likely to be the cheapest option? Many Thanks Steve