City romped to their third title in seven years, and Guardiola's first at the club, with a record points, wins and goals total in the 2017/18 season.
Asked which title he'd rather win, the manager told Sky Sports: "Premier League. No doubt.
"It will be a huge mistake to think: 'OK now we have the Premier League, we are now going to go for the Champions League instead'. Big mistake.
"To be out of the Champions League and win the Premier League again, I'd sign it now. The Premier League is the most important thing. It gives you the consistency to arrive at the right moment, the Champions League is so complicated the opponents are so good, all of them.
"The Premier League is the most important thing."