Aluko's left-footed shot from close range found the bottom left corner in the 66th minute to give the Cottagers a victory at the New York Stadium on Saturday.
And the Nigeria international was delighted that his strike put the Cottagers in place for a Championship play-off spot.
"Massive win today eventually breaking into the top 6. Grind of a victory. Favourite goal I've scored for Fulham so far. On cloud 9 when that went in," Aluko wrote on Instagram.
"Based on the 2 games against us I'm surprised Rotherham have gone down."
Aluko also picked Rotherham's Darnell Fisher as the toughest defender he has faced this season.
"They were very competitive and organised. I was in a battle straight away with Fisher today...as tough a 1v1 opponent I've faced this season... enjoyed the scrap.
"Now onto chasing 5th place."