[End game spoilers]
My protagonist is pretty smart (INT = 10)
So she can see that whichever way it goes there is going to be bloodshed, and a lot of it.
So (to misquote the 80's movie WarGames)
Fallout 4 is a strange game. the only winning ending is not? to play...
In practice this means the protagonist chooses to frustrate all factions attempts to bring weapons to bear on the others.
This requires 4 decisions to be made not to proceed at particular points, listed here :
Brotherhood of Steel
- Dr Li will never be persuaded to leave.
- Procter Ingram will never rebuild Liberty Prime.
- A certain synth will remain in ignorant bliss.
The Railroad
- Patriot isn't getting contacted, so the Railroad can't be attacked.
The Institute
- The journey to Mass Fusion will never be taken.
- BoS/Institute Hostilities will never break out.
The Minutemen
- Will happily march around their castle as their end game remains un-activated.
And frankly that where I'm going to leave the game's main quest lines.
It is a choice of tactical inaction.
Some synths will continue to escape (radiant quests) and general carnage is avoided.
I think that's a pretty good outcome.
In the meantime I'll collect all the magazines, bobbleheads and build all the settlements.
Pretty good place to be ready for DLC.