#1 John Terry
The most important thing that the current Chelsea team lacks on the pitch is a true leader. It is reflected in the way we have played. Defensively the team has been in shambles. In 21 games this season they have kept only 4 clean sheets and concerned 29 goals, a far cry from the glory days under Jose Mourinho when they kept a tight ship and knew how to shut out games.
Current club captain Cesar Azpilicueta doesn't start every game and is not much of a leader on the pitch. What the team needs is a commanding figure both on the pitch and inside the dressing room. Someone whose voice the rest of the players listen to. Someone who will aid Lampard in getting the best out of the players. No better man to marshal the defence and lead the team than club legend John Terry.
Stats are meaningless when it comes to JT as the sheer numbers are unimaginable. He played more games for the Blues than the entire current squad combined. Terry and Lampard are Chelsea's two greatest players ever with little separating the two.
JT is currently the assistant manager at Aston Villa and there have been rumours about Lampard bringing him back to Stamford Bridge in a coaching role. Whether those rumours come true or not, Lampard would give his right arm and more to have a player like Terry on the pitch, leading the team from the back.