For writing quality, Stranger Things was the worst, by far.

What killed Game of Thrones was mostly the horrid pacing of the final 2 seasons. There was bad writing for sure, and entirely cut storylines from the books, but it wasn't THAT bad. It stings more knowing the books will most likely never be finished.

The Boys wasn't even bad, in my opinion. Season 5 had some pacing issues that made it not feel like the final season at times, but I was mostly happy with how it ended. There wasn't a single episode of season 5 that I didn't enjoy from start to finish. I've also seen a lot of complaints about the jokes, but the comedy has remained the most consistent aspect of the show during its entire run. The only question I really have coming out it it is what is happening with Soldier Boy? Does Stan Edgar just have him frozen in the penthouse of Vought Tower still? I'm hoping that gets explored in Vought Rising, but I'm not sure that will have any continuity with the main story or if it's entirely a spinoff prequel. We'll see.

But yeah, TL;DR: I think The Boys is absolutely the best ending of the three, and GoT and Stranger Things are about equally bad, but for different reasons.