For the poll, I'd vote None of the above.
I've been saying for years that one way to do it is to adapt John Byrne's Terror in a Tiny Town (FF#236). The Fantastic Four would be the most senior characters (outside of Captain America and Sub-Mariner) in the MU/MCU but they went missing a short time before Iron Man appears on the scene. The story would play out similarly as in the comics...Victor would return from the past to gain revenge on his college rival Reed and snares Sue, Ben and Johnny in his scheme. At this point we would not see Doom....just a figure in the shadows. He would be gradually introduced into the MCU. Since Doom was also exploring the Microverse as far back as Fantastic Four, the concept of Liddleville and the Microverse could be combined. The FF bodies would be in suspended animation and the conciousness would be in tiny clones that went to explore the Microverse. But Doom sabotages the project and they became trapped there.
I don't think they should revisit the Fantastic Four's origin since it's been done in 2 of the Fox films. To cut to the chase, maybe the events of Endgame would result in the Fantastic Four being shuttled from the Microverse back to normal. How they got there could be told in flashback.