I have looked at your itineraries a couple of times. Both look like good trips. Both are very full of travel.Both are very tightly scheduled.
I am still digesting the details and trying to get a coherent set of comments, but can offer a few random thoughts..
Itinerary # 1 matches my own preferences better, particularly because you are not sleeping in as many different places. You will have more time to look around and walk around the towns. And, you can (if you must) reach the Jungfrau from Luzern if weather demands it, although it would be a long day.
It gives Alpine scenery and Luzern. Itineray #2 has three alpine communities... St. Moritz, Zermatt, and the Jungfrau region. Day 6 is pretty tightly scheduled, but the lake boat ride would be fun. Not sure how far it goes down the lake, so my comments below about seeing the southern part of the lake...in daylight, still hold.
Long term members of this forum know that I would rather spend my time at places other than the Rhine Falls....I have seen a lot of waterfalls. I still have not seen all of Switzerland, after 35 years of visiting the country. However, Spring is a good time to see them, because the snow melt and spring rains create a strong water flow. Nonetheless, especially on itinerary #2, the first day is very very full, and I'd give some thought to skipping either the Rhine Falls or the boat ride on Lake Zürich (der Zürichsee).
If I had to choose, I'd prefer a lake boat ride on Lake Lucerne, compared to Lake Zürich. In itinerary #1, day 4 might allow more time on the lake, especially at the southern end, south of Vitznau down to Flüelen. There are many possibilities, but, for one example, you might take a train to Flüelen, boat to Vitznau, cograil to Rigi Kulm, cograil or walk back down to Rigi Kaltbad, cable way (die Luftseilbahn, abbreviated "LSB" in the timetable) down to Weggis, 15 minute downhill walk to boat landing at Weggis, boat from Weggis back to Luzern. Since the boat schedules in the Spring may have fewer trips, I'd watch that last connection at Weggis carefully. I might rearrange the order of the trip, but would try to get the boat ride on the part of the lake from Flüelen northward. You could do it in either direction. The cograil from Rigi Kulm down to Arth Goldau is fine, but, in my opinion, is the least interesting of the three options for the Rigi excursion.
Depending how much time you choose to spend up on Pilatus, if you choose that option....there is not a lot to do up there....you might add lake boat time on that trip as well.
Pilatus is a much more dramatic mountain than the Rigi.
Take a look at some of the recent trip reports in that section of the forum- such as -
Look at her pictures.
Also, the attached from Anjan Ghosh's posts.
Is the cograil up to Pilatus Kulm running on your dates? It is closed during the winter Check the timetable from Alpnachstad.
One thing to remember...for better communication and use of the timetable, please spell the names of towns correctly:
Gimmelwald, Grindelwald, Lucerne (or Luzern, German version)