If you want to find out why trains are so popular in Switzerland, do rent a car :-)
Anyway: What the best offer is, is for you to decide. Only you know what your definition of “best” is. But what you can do is just look up the prices on sbb-tickets.cc for the trips you want to take.
And then you can look at what different passes would cost. And decide for yourself. My guess is that you are probably best off buying tickets, with Lugano - Luzern best bought in advance so you can get a Supersaver ticket.