Guardiola famously clashed with Jose Mourinho when he and the Portuguese were the respective managers of Spain's big two, Barcelona and Real Madrid.
But Guardiola feels the level of competition City has faced from Liverpool in recent years has been above anything he had to deal with at Barcelona when he was competing with Madrid for the Spanish league and Champions League titles.
"In the last five years they have been the biggest opponent," Guardiola said Friday about Liverpool. "Jurgen, as a manager, has been the biggest rival I've ever had in my career and I think what both teams propose is good for football ... I will remember my period here, when I'm retired watching and playing golf, I'll remember my biggest rival was Liverpool, for sure."
City holds a one-point lead over Liverpool heading into the encounter at Etihad Stadium.
"It will be a massive, important three points but there will still be seven games, 21 points, and a lot of things involving the Champions League and FA Cup (to play for)," Guardiola said. "But of course it is important."
Sunday's match is City's second of four games in an intense two-week period that also includes both legs of a Champions League quarterfinal match against Atletico Madrid and another meeting with Liverpool, in the FA Cup semifinals.
Guardiola dismissed suggestions he would be happy with a draw against Liverpool, sarcastically saying: "We trained today to sit back for 90 minutes, to get 0-0, 0-0, 0-0!"
Unlike Guardiola's rancorous rivalry with Mourinho, there is a huge amount of respect between him and Klopp.
"Jurgen makes world football a better place to live with his message," Guardiola said.
In turn, Klopp has described Guardiola as the best manager in the business.
"Thank you so much, but I'm not," Guardiola said. "I would like to tell him I'm the best but I'm not."
