Who's position does he take?
He takes Zanetti and Tiago's position as the "playmaking defensive central midfielder." Essentially the Pirlo to our Gattusos, Sissoko or Nocerino.
Honestly, I think he'd make a nice partnership with Sissoko. Of course, Zanetti could probably challenge for the pure defensive position as well.
We have to admit, if the choice is between Diego, Lampard and Aquilani (with an offchance for VDV), Lamps might be the least preferred, but we're at least talking top echelon players (or in Aquilani's case, potential to be top echelon). We're not talking second tier players or guys well in their 30s, like Senna.