Whilst Rooney has improved, I don't think he has improved by leaps and bounds because IMHO he was a terrific player at the end of last season. It is a complete mystery to me why Butcher was reluctant to play him at the end of last season and the start of this season.
Others like Hayes, Eagle and Cox have also improved but for me it is not about individuals improving, it is the team as a whole. It took a while for the team to gel but they are playing well as a unit now and that makes a difference.
In particular I think the back four (or five) as a group would jointly get my vote. Although they are very experienced, I thought both Tokely and Munro looked very jaded at the start of the season and when he came into the side I thought Golabek had lost a yard of pace and was probably past his sell by date but all three have improved considerably as the season has progressed and with solid contributions from Proctor and the improving Bulvitis we have now developed a very solid back line again. This has been the key to the good run because we have been scoring goals all season, but in the first half of the season we were shipping far too many at the back as well.