Redknapp said: "James is fantastic. Without a top, top keeper you are nothing and he's the best one around at the moment."
He added: "For me he's the Ronaldo of goalkeepers, someone who does that little bit special.
"The England thing was difficult. He was caught in no man's land and it was virtually a collision between him and Nicolas Anelka. But I don't believe it has upset him. He just moves on now.
"When I knew there was a chance of signing him last season I jumped at it. A lot of other silly names were thrown at me but he was always the one.
"He does fantastic things even in training, saving one-handed after diving full length, things like that. He moans on and on when we've conceded from a free kick but that's because he is determined to get it absolutely right.
"He's more concentrated now. Sometimes at Liverpool he used to make mistakes because he lost concentration and came flying out for crosses that he could never get. I think he used to get fed up and want to get involved in the action, but he's learned from that now."