2018 was, as
@el niche said, faster paced, and yeah the AI is quite dumb, so you could sometimes get quite easy goals.
The mechanics are a bit more suited for some co-op kind of match, and the game can be a bit weird at times, with a few bugs.
2019 is too heavy and also quite scripted at times, so didn't really like it, feels like almost all goals can be scored in the same 2-3 ways, and other ways to score will be blocked by the AI
2020 was just OK at best, it was also scripted but I think the earlier versions of Pes 2020 were a really solid base, and it could have been improved over time for a good PES 2022, but we don't talk about that. As
@Flipper the Priest said, the different iterations make it difficult to really compare, but 2018 and 2019 had less of the differences I'd say, compared to PES 2020 early versions and final version, which I didn't like, it feels too scripted and either too heavy or too fast at times
2021 was the exact same man, I really liked the game for the first 2-3 months of the release, then after like 2nd DP update and all that, I lost interest, all that kept me going was some Master League saves, which I managed to go 2 seasons with Ajax, and 4 with Barcelona, and then I stopped
The final version of 2021 really fails to keep any interest in me
I would rather play PES 2013 , 2014 or 2015 or 2011
I think if you really want to choose between these games, you would just have to play them yourself.
But if you ask my opinion, PES 2018 and 2021 are the good ones out of them (I mean decent and playable at least and not too scripted and heavy)