If you break down their goals count it will be like this :
Aguero : 20 Goals (1 penalty) in 32 Games (league) \ 3 goals in 4 games (cup) \ 4 goals in 5 games (Europe).
Rossi : 18 Goals ( 4 penalties) in 36 games (League) \ 3 goals in 5 games (cup) \ 11 goals (5 penalties) in 15 games (Europe)
And also In the league:
Aguero scored in 14 different match, 4 braces and 1 hattrick.
has been Man of the match in 8 games.
Rossi scored in 16 different match, 2 braces.
Has been Man of the match 6 times.
In Europe Aguero scored in 2 games, a brace against chelsea in CL, and a brace against sporting in EL. he played 5 games in total.
but Rossi did go far in EL with his team, he played 15 games in EL, Scored his 11 goals in 9 different games. as I said, 5 of his goals were penalties.