I would like to spend a couple of days at Grinderwald, what is the best travel method train, bus or car ?
sbb.ch/en is your friend
Most definitely train.sbb as mentioned above, plus look at
There you will find a lot of good info. and links about rail travel.
And if you have time, go via Montreux and Zweisimmen to be able to enjoy the very nice http://www.goldenpass.ch/en
Using sbb.ch/en, just add via Zweisimmen in the search.