For me its got to be either Downing or Henderson. Both went from overly priced transfers to players who deservedly earned a place in the starting XI. Although they still don't quite play as good as they're price tags suggested, they're still better than 12 months ago.

So which player has improved the most this season at your club?

De Gea, Rafael,

Rafael

Tello

Cahill and Torres

Mangala, without doubt. Very young, and has impressed so much he's been called up for the French national team. Him and Varane will be a wall for France in not too many years.

Alex Sandro and Jackson Martinez deserve to be mentioned as well.

Jenkinson = by far & away the most improved player at Arsenal.

De Gea and Rafael

@Footaholic
I think Koscielny deserves to be on the list,too

Hint: He scores when he wants, he scores when he waaants...

Adebayor?

Hahah :D

Tello for me

Balotelli

Ramsey, Koscielny and Jenkinson

Dani Parejo. Hated in october but loved now in the late part of the season

Like awais said, Torres and Cahill have improved A LOT. Especially Torres :). I would also add David Luiz. He has become a monster near by the last three months of the season. If loaned out players also count then Lukaku is in my list as well.

It's jenkinson. Ramsey also improved a lot.
Koscielny last season was already world class.

Alexis towards the end of the season. Maybe Thiago as well?

Ramsey.

Luiz