I'd probably pick Endgame.
Why?
Because if I could never know what happens in the ones I didn't pick, passing on Endgame would screw up ALOT of future movie viewing, conversation, & media/entertainment consumption.
GoT (TV version)? This really isn't a topic of conversation in my circles except for around the 8 weeks or so per season. And I don't go out of my way to read about it/discuss it on-line. It also doesn't tie into anything besides its own previous seasons. So not ever knowing will not be much of a hindrance.
Besides, eventually the book series will conclude & I'll just read the actual story.
SW Episode IX? Well, I enjoyed 1/2 of TFA and virtually none of TLJ. Since TROS continues this downwards spiraling story.... 9 Hells, I don't even like this ones title! So not knowing could only be a blessing I'd guess.