Off the top of my head:
-2004-2005 Liverpool: Didn't do well in the league, but in the CL's, they have in my opinion the greatest CL run of all time. They took out a world class Juventus team, beat 95 point Mourinho Chelsea team in semi finals, and than beat a legendary Milan team.
- 2014 to 2016 Atletico Madrid: Won the league against prime Real Madrid and Barcelona in 2014. Seconds away from winning the 2014 CL final against a monstrous Real Madrid team that wiped the floor with Bayern 5-0. 2016 --> They knocked MSN Barcelona in their prime in UCL, knock out Pep's Bayern team (best team in the world that year in my opinion), and only lost on penalties to Prime Real Madrid team. Finished only 3 points behind MSN Barcelona in league.
-2018-2020 Liverpool: Pushed the greatest PL team of all time (Pep's man city) to the absolute limit getting 97 points in 2018-2019. Far less spending budget that Man City. Win the 2018-2019 CL. Every player on that team pushed their absolute physical limits. The intensity they played almost every game that season was insane. A major injury to just 1 or 2 important players would have completely derailed that season, but the important players managed to stay healthy despite the pressing intensity. The next year, they win 25 out of the first 26 games of the season! Pretty much ending the PL title race by January.
Come on man, 2020 Liverpool was one of the best in the history.