Swiss Pass or Eurail Global Pass ?

I am planning my 2nd Europe trip and my duration is flexible. I missed to visit Switzerland during my last trip because I cannot decide on the train pass. I plan it for my next visit since I want it to be the highlight of my trip. My whole trip will be around 2 to 3 months using a eurail global pass but I am not sure if I should get a seperate Swiss Pass for Switzerland or just use my Eurail Pass. I understand some of their services are not similar and as my duration is flexible, I hope to make a choice that make the best of my budget. My days in Switzerland is not decided yet.
I am more interested in outdoor scenery, journeys and day walks; and less on city scenes. So I probably will not stay to visit any city for more than a day unless I use it as a base for nearby trips. I wish to do all the 4 scenic rail journeys or at least 3 of the more popular.

Please me on whether I should just use the Eurail or get seperate Swiss Pass.

If I use a seperate Swiss Pass, I will place Switzerland at the beginning or end of my trip.

Thank you for any advice.