The best man to replace Steve Waugh was Mr Darren Scott Lehmann , who was correctly chosen to replace him.Best replacement for Steve Waugh in the Aus test squad
However I think you mean the best spare batsman/allrounder , in which case it would be a race between about 8 contenders -
Love , Clarke , Symonds , Hussey , Hussey jnr , Hodge , Watson & North.
Probably Love for me , deserves a chance ahead of the Hussey's , Symonds & Hodge as he's played tests already & done nothing wrong.
Clarke & North arent ready for test cricket yet & Watson's game isnt really suited to Sri Lanka.