Mar 18, 2012 - 12:35 PM
In my view Lauterbrunnen and Grindelwald are about equal as starting points for a Jungfraujoch rail trip. I've traveled from both towns to Kleine Scheidegg (part of your train trip) many times, although I never stayed in either of these towns.
Maybe Gindelwald is a bit more touristical? But if you have one day left for other activities Lauterbrunnen could be the place to be. You could visit the nearby Trümmelbach waterfalls, take the cable car from Lauterbrunnen to Grütschalp, from there go to Mürren (by train or by foot) and back to Stechelberg by cable car and Lauterbrunnen (by bus). Another option would be to visit Schilthorn (amazing views, if weather conditions are good).
On the other hand, from Grindelwald you could take the gondolas to First, or the cable car to Pfingstegg, or visit the gorge of the "Unterer Grindelwaldgletscher".
Conclusion: I can't advise you any further!