In the week before last season’s Champions League quarter-final first leg, Pep Guardiola was attempting to prepare for a match against Everton. But he could not help his mind constantly going to their neighbours making so much noise across Stanley Park.

“The forwards of Liverpool are good,” the Manchester City manager said. “They scare me. They’re dangerous.”

His assistant Domenec Torrent then interjected, as much to offer encouragement. “I watched our game yesterday when we went there and lost [4-3 at Anfield],” the coach is shown as saying in the ‘All or Nothing’ documentary. “They played on another level. If you want to beat them, you have to work to do it. If we are at our best, we are better than Liverpool.”

But City were unable to prove that in the Champions League. And the results – not to mention the performances – from those games has now ensured that there is a defining question in this developing rivalry, which could also prove to be the defining issue of the season

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Who, in a very fundamental way, are actually the better team?

While City have obviously proven they are the better side over the long term by winning the league, there has been a growing argument Liverpool’s best performance on an individual night - to invert Torrent’s point - might be at a higher level. The fact Jurgen Klopp’s side have won the last three games between them bolsters this argument, as does the run to the Champions League final, especially with the way such games evidently bring out the best in them.

Their problem has been sustaining that level.

That in itself only adds another edge to Sunday’s showdown at Anfield. Another twist.

Klopp has so evidently looked to recalibrate the make-up of this Liverpool side, so as to give them that greater stability. They haven’t yet been anywhere near as rampaging as last season, but they have been much more resolute.

That was a process that started with the signing of Virgil van Dijk, but has clearly progressed, as the side has become more cohesive all over. Liverpool conceded 28 goals in the 24 matches without the Dutch defender last season. That dropped to 10 in 14 by the end of the campaign, and is currently at just three in seven right now.

It does generally feel that Liverpool just don’t leave open the same space, even if that slight withdrawal means they don’t quite open sides as readily either. It has meant steady if incomplete improvement, with the late equaliser against Chelsea showing a new resilience and the unusually tepid defeat to Napoli showing the readjustment is ongoing.

It has also meant one big tactical question ahead of this match is whether Liverpool go at City as abrasively as they have done in the many matches where it’s been a proven success… or whether they rein it in slightly, with the approach that they are trying to make this season a success with.Pep

Pep Guardiola was worried by Liverpool's full-backs (Getty)

The feeling from Melwood is that they will raise it, go at City again.

And that might be to their benefit, because it is not the main tactical question to this game.

That remains how Guardiola will set up against this Liverpool side – a side that have so clearly got into his head. It is said to have again consumed him this week.

Underlying this question of who is the better team, after all, is the question of whether Liverpool are just specifically suited to playing against City; whether their particular best qualities just do the worst damage to the Catalan’s side. That is not quite the same thing.

Van Dijk's arrival has made a huge difference (Getty) (Getty Images,)

Another revealing little detail from that exchange with Torrent was Guardiola admitting “our wing-backs can't cover their wing-backs”.

It was what left City so destructively open in the January 4-3 defeat that was much more emphatic than the scoreline indicated, but the initial response wasn’t much better. So clearly conscious of that for the first leg of the Champions League tie, Guardiola looked to slow the game right down by retaining possession and being much more cautious, but it had an entirely unintended consequence.

It just slowed City right down, and meant they weren’t psychologically ready for Liverpool still being able to up it.

They were caught cold, as a white hot Anfield saw one of its great home displays. This was why people are saying Liverpool’s best is better. This peak.

This pair could prove key (Liverpool FC via Getty)

That is however a claim known to rankle with some at City, who have so often touched sublime levels. The feeling is they actually haven’t offered their best in any of these games, and if they do - and use the ball in the unique way they can - it will make Liverpool’s energy with it so much less relevant.

Guardiola is known to be highly conscious of the need to work out how to beat Liverpool this Sunday, to get to that best against them, but that's for his side’s own mentality as much as any advantage in title race. He needs to prevent a complex developing about Liverpool, but it's complicated.

This is another element that fires this debate, and has so elevated this fixture: the tactical difference between the teams, that so corresponds with their wider qualities.

If the feeling is Liverpool are unsustainably brilliant on individual occasions, they also hurt with you lightning blasts. City meanwhile swarm a side and then pick them apart, just as they swarm a league campaign and gradually just pick up a critical mass of points.