Which side of the train is better to have great views.

I am not sure about a good side from Milan to Luzern, but there appear to be no more direct trains, so you will have to take a transfer. If you take the EC train, seat reservations are required and you will have to transfer at Arth-Goldau.

But if you take the RE 80 from Milano Centrale to Lugano and change to the IC train to Luzern, seat reservations are not required, so you can freely move one side to the other if seats are available. These connections leave Milano Centrale at 43 past the odd hours (7;43, 9:43, etc). This way is also 13 minutes faster than the EC train. Still you might get a better price on a discount ticket with the EC train. Just an option to consider.

Luzern to Interlaken, definitely the right hand side for the better view especially on the section over the Bruenig Pass and down to Meiringen, where you will see the Reichenbach Falls across the valley. That is where Sherlock Holmes and Professor Moriarty fought to the death, or so I have been told by Dr. Watson. At Meiringen, you will change direction and now you will be on the left side, which is also the best for views across the Brienzersee and many water fall views there. The hotel at the base of one of those falls was used as a set filming "Band of Brothers" as a stand in for Zell am See.

Having said that, i would say the Brienzersee would be the better boat ride.

For Luzern to Interlaken and from there to Zurich you do not need reservations. So just don’t bother with them. Just get in and sit wherever you want.

And Interlaken to Zurich depends on which way you go, via Luzern, or the fast way via Bern. I'd say the right hand side either one. Via Bern, you get nice views of the Thunersee, but after that, nothing special. If you are on one of the morning direct trains (7, 9, 11) you change directions at Bern, so you will be on the left for that leg.

Via Luzern, right hand side again.

Thanks everyone. Im looking at EC train from Milan to Arth Goldau and from there to Luzerne.
From Luzern to Interlaken I will take a direct train with the shortest duration. And same goes with Interlaken to Zurich. The day I've my train from Interlaken to Zurich , same evening (5:30pm) I will be flying out of Zurich to Prague. Wanted to know if it is okay if I take a train around 11am from Interlaken which arrives at Zurich Airport around 1:15? Also how's the punctuality of the Swiss trains? and anything else to keep in mind as I've a flight in the evening?

Before the pandemic I used to travel to ZRH about every other week. Always by train. And I never missed a flight. The trains are very reliable. For a flight to Prague I would personally aim to be around 1 1/2 hour before the flight. Zurich is efficient, and you do not need to go through passport control, just security, as this is a "domestic" flight.

So in this case the latest practical departure from Interlaken would be at 13:30, but I would pick the 13:00 as that is one change less. Gets you to ZRH at 15:14

Thanks WengenK, I wanted to have few more hours at Interlaken as we will be there for around 1 n half days.. may be 1 extra hour..

Regarding the Swiss train tickets, do the price of the tickets increase as we get closer to the travel date or buy on the day of travel? or is there any advantage of advance booking? I also suppose the Super Saver fare might be useful if I know which exact train to avail? or I go with the normal fare ticket which gives me the flexibility of the entire day?

Well, don't go to Early. For a 17:30 flight check in will not even be open at 13:15. So being there earlier than 15:00 just wastes your time.

Standard tickets are always the same price, an second or a year before departure. Supersavers are only available in advance, and are limited in availability...