Paris to Switzerland (Lucerne & Interlaken) and then on to Venice. What is the best route?

For your itinerary options you've listed, I would select Paris-Lucerne-Interlaken-Venice, but I definitely would replace Wengen with Interlaken. The prettiest scenery is the Lauterbrunnen-to-Wengen train. Interlaken would be like heading to Disneyland but stopping your trip at the entrance gate.

Before you solidify your plans, consider how many daylight hours you will be at each location. If you're spending a large part of a day traveling to the next location (your locations are very spread out), you're missing out on a lot of vacation time having fun. Each one is about 7 hours apart by train; we aim for no more than 3 hours between locations. Are you also planning just 2 days in Paris & Venice?

rosyashish, there are 6 trains a day from Paris to Switzerland which can get you to either Luzern (local spelling) or Interlaken.
The current timetable is here: http://www.tgv-lyria.com/sites/default/files/pdf/BROCHURES_CO/TIMETABLE-2016-ch_fr-TGV-LYRIA-EN.pdf
For most places in central Switzerland you would change in Basel. There are connecting trains from Basel to Luzern or Basel to Interlaken ever half hour.
I agree, do not stay in Interlaken but somewhere further into the mountains, Grindelwald, Wengen, Mürren etc. All a short train ride from Interlaken.
Consider staying in either Luzern or (near)Interlaken, but not both. You can do one from the other as a day trip, via the scenic Brünig Pass railway.

When continuing to Venice, both Luzern and Interlaken are equally inconvenient, because of lakes and mountains in the way!
Go to www.sbb.ch, type in Luzern or Interlaken, to Venezia and a date and time and it will give you the train times.

If viewing mountain scenery is a priority, go Paris-Interlaken-Luzern-Venice. Don't get hung up on that 18:23 direct TGV. Taking an earlier train, like the 14:23 which will take the same time with a comfortable connection in Basel and get you in in time to still catch glimpses of the Eiger and Jungfrau as you approach Interlaken (provided the weather is clear and it is late spring or summer when the sun is still up at 19:30).
The train from Interlaken to Luzern is especially scenic. So is the train from Luzern to Milan which only has one major tunnel at the Gothard Pass. The route from Interlaken to Milan has 2 very long base tunnels which go completely through the mountains. Its fast, but very dark.

Did the same route back in 2000, and went from Paris - Interlaken - Luzern, then took train to Zurich to catch night train to Venice. Alas I believe that night train has gone, but I guess you could go via Zurich.

Would recommend that you prioritise the Bernese Oberland (Interlaken, Wengen, etc) over Luzern. As previously mentioned, a daytrip is fine for Luzern, or an overnight stop before heading on to Venice. Enjoy!

Thanks to all of you for your great input. To clarify we are spending 4 nights in Paris and then heading to Switzerland for 4 days and then on to Venice, Florence and Rome. We would love to stay in the small villages outside Interlaken but it appears that the trains take about 1/2 hour to 45 minutes and since we plan on taking early morning train from Interlaken to Venice it will not be convenient.

Our plan is take early morning train from Paris to Lucerne and then spend day in Lucerne enjoying the lake and the city. Next day go to Mount Pilatus. The next day take early morning train to go to Interlaken for 2 days. On our second day in Interlaken we would like to do the top of Europe excursion. I believe that train also takes you to some small villages that we could explore.

If someone could suggest what best to do the other day we have in Interlaken I would appreciate it. It appears from the previous comments that spending the day in Interlaken itself would be unwise. What other small villages are close by that we could get nice views of the Alps? Places we could go after lunch the day we get to Interlaken and come back easily by evening. Also reviews/comments about top of Europe would be appreciated. Lastly how is Mount Pilatus? It appears to be a different type of excursion from top of Europe and so we thought we would do both. I apologize in advance for the lengthy email.

Never been to Pilatus, so can't say for sure, but doubt it's got much on the Bernese Oberland. Mt Titlis is nice though - take a train to nearby Engelberg and ride up the 3 different gondolas/cable cars (including a rotating one) to the wave shaped summit. Plenty going on in the mountain station, like a large glacier grotto, restaurants, shops etc, but outside you can take a ski lift down to the Glacier park, where there is summer sledging with free sleds, tubes and such to ride on as many times as you like, with a moving walkway to get you and your ride back to the top of the slope. This is great fun! The cloudy day only added to the thrills for me as I couldn't see where I was going! Very safe though. There's also a new cliff-walk suspension bridge that looks good.

Interlaken is a nice town, I've stayed there twice. Wouldn't spend much time there, although a stroll along the main street seeing paragliders take off from Harder Kulm and land in the park is fun. As for where else in the B.O.,, the Lauterbrunnen valley is hailed as one of the most beautiful in the world, with high sides and many waterfalls - you could do a gentle walk along the valley floor a little way outside of the main village, cross the river and circle back easily in half a day - or catch the cog wheel train from Wilderswil (just outside Interlaken) up to the Schynige Platte, where there is a lovely alpine botanic garden with great views of the mountains.

For a full day, you could visit Grindelwald, take the gondola to the Mannlichen ridge and take a level but scenic walk to Kleine Scheidegg, which is near the north face of the Eiger, carrying on to Eigergletscher (if you feel energetic!), then walk left along the Eiger trail to one of the stations, or right towards Haaregg and another station. Another option is the First Fun Package - take the Grindelwald to First cable car, then the zip line down part of the way, walk the middle section, then take a Trotti (scooter) bike the rest of the way to Grindelwald. There are so many more things to see and do in the Berner Oberland, you could spend a week there - which is what I'm planning for this summer!