New housings, preferably - provided you can avoid anything printed with "Jagwire" or "SHIMANO" on the outer casing.

An exception to this would be older Raleigh-made machines that originally came with Sturmey-Archer ribbed housing, or pre-TI Industries machines that used silver housing - I generally keep a stock of good used cable housing in both black and white for the former, and I have a selection of NOS, 1950's/60's aftermarket Clarke's silver cable housing for the latter. Considering that the early machines use double-soldered-end cables, one must keep these cables on hand if they keep any of these machines in their fleet.

-Kurt