The best formation that suitable with the current squad we have is 4-3-1-2, the alternative is 4-2-3-1, or perhap the more risky 4-3-3.
These are the Starting XI for me when everyone is healthy.
4-3-1-2:
Buffon
Zebina Cannavaro Chiellini De Ceglie
Sissoko Melo Marchisio
Diego
Amauri Del Piero
4-2-3-1:
Buffon
Zebina Cannavaro Chiellini De Ceglie
Sissoko Melo
Camoranesi Diego Giovinco
Trezeguet
4-3-3:
Buffon
Zebina Cannavaro Chiellini De Ceglie
Sissoko Diego Melo
Iaquinta Amauri Del Piero
*If Melo transfer did not go through in the end then replace him with Tiago in 4-3-1-2 and Marchisio for the others.