They've been the heart of most things their teams have done well this season - and neither Manchester City or United have started the season in scintillating fashion, with just 16 and 14 points respectively from nine games.
The red half of Manchester have performed like a delayed train service so far, whilst the blue half's start can be more comparable to a wind-tunnel that keeps switching on and off.
At times - including the brilliant 4-1 win over their city rivals - the Citizens have looked close to unstoppable, putting together some wonderful flowing football through Samir Nasri, David Silva and Yaya Toure with Aguero at the heart of it all too.
These performances, however, keep being accompanied by the likes of the drab one in the 0-0 draw with Stoke City and the second-half capitulation away to Aston Villa.
For United, it's been all about Rooney - that man who it seemed was destined for the exit door over the summer following a turbulent break.
His attitude, work-rate and class have been second to none in the league.
The forward has been exemplary, digging David Moyes out of nearly every hole the team have dug themselves into so far.
While the rest of the team waits for each other to sort themselves out, Rooney has been a true driving force - the main man keeping United ticking along.
So how do they compare?
It's seven goals and four assists so far for Aguero, whilst Rooney has scored just four (also with four assists).
It is fair to argue that Rooney's shortage of goals compared to Aguero is down to the way United have played this season - average for large chunks.
United have only scored 14 goals compared to City's 21, which of course included four in the Manchester derby - where Aguero bagged a brace.
It's in those games - where City have looked at their free-flowing best - where their mercurial Argentine has shone most brightly.
His first against the champions was a wonderful piece of improvisation, while he sprang West Ham's offside trap with ease before also providing a wonderful assist for David Silva.
Rooney, meanwhile, has been carrying the can while his Red Devils continue to underwhelm.
Until the arrival of Adnan Januzaj against Sunderland, nobody else in the team was providing any flair, with the wingers performing desperately poorly so far and Robin van Persie also starting the season slowly.
Van Persie has got back to some sort of his goalscoring form now with two in his last two games, but it's so far been the England forward who has had to bear the weight of everything attacking-wise for United.
His contributions include free-kicks against Manchester City and Crystal Palace as well as two assists against Swansea - back when his long-term future was still in some doubt.
He was also outstanding against Stoke City, providing the perfect header to fire his team level on Saturday and propel the team toward Javier Hernandez's winner, as well as assisting Van Persie's effort himself.
So to say Aguero has been the better player based on numbers alone is too simplistic.
However, the style of the son-in-law of Diego Maradona is an art form in itself.
He is incredibly comfortable with the ball in tight spaces, linking up superbly with Silva, Nasri and co. as well as scoring every type of goal you could wish to see - including that stunning near-post strike against Chelsea on Sunday.
Rooney also shows the ability to score a variety of goals - headers, free-kicks, tap-ins - and you also have to consider that the Scouser plays a more supporting role to Van Persie for the majority of the time.
Although Aguero operates behind Alvaro Negredo, it is still arguable that he is considered the main-man of City's attack.
To separate them on performances this season is an almost impossible task, and quite simply, comes down to a matter of opinion.
Watching them both in such scintillating form, however, is only a good thing for the Premier League from a neutral perspective.
The league needs players like Aguero and Rooney at their very best.
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