Been Sunday to the Jungfraujoch (with Sparpreisoffer from SBB, paid with Halbtax 116 sfr return), awesome mountain, trip takes around 4,5 hours one way.Don't do the trip via Grindelwald, because the big bunch of People from the
coaches start the journey in Grindelwald-Grund. There is anonther possibility(Lauterbrunnen/Wengen)
If the weather is fine at jungfraujoch , i can recommend do a reservation for the trip to/from Kleine Scheidegg to the Jungfraujoch (10 sfr each way/Person).
The weather on Sunday was awesome up there,can highly recommend going up
there.
On the way return we had to go via Luzern(From Interlaken) back to Zurich, takes one hour longer, awesome scenery there.