When considering ice screws and other winter climbing protection, it should be emphasised that by far the best ice climbing protection gear is rock climbing protection gear. If you can place wires, nuts or slings, then do - they will be far stronger and quicker to place than most ice gear. And despite the general preconception that cams are useless in winter, they are actual well worth carrying as long as they are not placed in icy cracks.
If no rock gear is available then ice screws (in good ice) and pegs are the next best options, and only as an absolute last resort, Warthogs, deadmen, snow stakes and hooks.
Having said that many hard ice routes such as Orion Direct (V) on Ben Nevis require a rack of at least six screws minimum, two for a belay, two or more for runners and two for the next belay. Also warthogs or ice-hooks are about the only thing to use for belaying on on some frozen turf areas such as the top of Ben Udlaidh.