Falcao arrived at United on loan from Monaco in September, but has managed just four goals in 12 Premier League starts under Louis van Gaal.
"They [United] have a number of very talented strikers," said Aguero at a sponsor's event. "The one who in his career has been the most predatory is Falcao.
"He isn't having an easy time this season, but I really admire his commitment and his class and qualities are permanent.
"He is probably one of the most naturally gifted strikers in football at the moment."
United host City on Sunday sitting a point clear of their local rivals in the Premier League. However, Aguero still questions whether Van Gaal's men can turn in a good enough team performance.
"They are a team with a lot of great individual players, who can form an incredible unit when they work well together," he added. "But this season that has not always been the case.
"Some matches they don't seem to play at the maximum, with the attacking qualities that they have in the team. But then in other games, they have really shown that those qualities, so they are a bit unpredictable.
"We know we will have to be at our very best to beat them - there's no doubt about that."
