I think TMac plays marginally better D than Pirlo in that he hustles his ass off to make a play he's not fast enough to make
Going by last season, because i dont think either of them have enough games this season for it to be relevant, Pirlo averaged 2.2 tackles per game whereas TMac only averaged 1.3.
This season Pirlos average is 1 per game whereas TMac is slightly better at 1.1.
Offensively Pirlo is also the much better choice, he actually knows how to hold onto a ball and complete passes.