For the most part in 2005, Kaka was better. Gerrard was just on the winning team.
And yeah, Pirlo has always been masterful, but again, the inconsistencies of Milan have held him back from keeping a consistent form. Players like Seedorf, Inzaghi, Pirlo, Kaka, and Maldini are no doubt great players, but together they don't seem to be able to keep each other going. Gerrard has always had the help of a much more team oriented Liverpool; not to take anything away from him. His defensive qualities are probably what puts him over Kaka anyway.