>> Move to either Lanterbrunnen or Wengen and use it as base for 3 nights. Which would be better in terms of travel via train accessibility?
Train accessibility isn't everything ;-)
Wengen and Mürren have more spectacular views than Lauterbrunnen, as they are located high above, and overlooking, the Lauterbrunnen Valley. They are also car-free, which gives them a special ambience.
Wengen is only 12 minutes on the train from Lauterbrunnen, and the ride up is spectacular.
Mürren takes a bit longer to get to (23 to 32 minutes), but the ride (whichever of the two possible routes you take) is also spectacular. There is a good description of how to incorporate both routes in rockoyster's post of Jan 27, 2018 - 2:11 AM on the following page:
>> Would like to cover Grindelwald,Jungfrau ,Pilatus and “top of Europe”
Pilatus is near Luzern. Grindelwald and the Jungfraujoch are near Interlaken.
The Jungfraujoch and "Top of Europe" are one and the same place. "Top of Europe" is just a marketing term for the Jungfraujoch.
You shouldn't miss Wengen and Mürren when you are in the Jungfrau Region. The Schilthorn is also a wonderful trip, and is free in 2018 if you have a Swiss Travel Pass.
I have attached some photos taken from Wengen and Mürren. If you are interested, you can see photos taken from the Schilthorn (and Jungfraujoch) in my post of Mar 1, 2017 - 10:12 PM on the following page:
Lauterbrunnen is the village you can see at the bottom of the valley in the photos taken from Wengen.
What time of year are you going? Some mountain transport does not operate in the winter, and some closes in the off-season for maintenance.