I would say it depends on the track arrangements at each end of the line.
Here are two "real world" examples of switchbacks and how they were handled:
The Mount Hood Railroad has a switchback a few miles out of their base of operations in Hood River, OR. The switchback is near the beginning of the railroad, and all trains leave Hood River with the engine pushing the train up to the switchback. This places the locomotive at the head end of the train for the rest of the trip over the line.
The switchback that I am most familiar with is the one on the McCloud Railway Company, which also remains in service to today. When the railroad was built there were two switchbacks on the main line, but a big fill replaced one. Through most of the steam era this switchback was dealt with by placing locomotives at both ends of the train. The diesel era started with trains operating in reverse up to the switchback, then leading engine first the rest of the way over the hill...however, this changed after a few years, and trains now leave McCloud engine first to the switchback, then backing the rest of the way up and over the hill. An added bonus of this method is that it puts the power on the head end once the train reaches the interchange yard in Mt. Shasta, meaning that switching is as simple as backing the outbound cars into one track, picking up the inbound cars from another track, and then leaving engine first, which puts them backing the train into the McCloud yard at the other end of the trip. From a model railroad standpoint this method deserves some attention, in that it would significantly cut down on the tracks needed at both ends of the line (you wouldn't have to try to fit in run-arounds at one or both ends).
Timber Times magazine ran a series called "Modeling an Oregon Logging Road" that ran in six or eight issues in their early issues. No specific operation was featured, but the series did look at various prototypes around the state to draw inspiration and ideas. One of the articles was titled "Dealing with a Switchback". I have not personally seen this article, but if it is written at the same quality of the others in the series that I have seen it should be a good one. This issue is still available, at least in photocopy form, from Timber Times (go to
http://www.timbertimes.com, look for the Magazine link, then go to Back Issues).
JD Moore
Elko, NV
http://www.trainweb.org/mccloudrails
http://www.trainweb.org/highdesertrails