I'd say almost the same. Except Cassano never really used more than 60-75% of his talent. Aguero is probably already better than Cassano because he has used his talent.
And to whoever said a few pages back that Cassano is the best player in the Serie A is wrong. That title belongs to either Ibra, Eto'o or Sneijder. Although in terms of pure skill over a whole career probably Del Piero, Pirlo or Totti