After 12 Premier League games, which summer signing has had the biggest positive impact on his new team?

I really think it's a toss up between a, b, and c all those three have had a big impact in their teams... Riera has given you greater width then you have had for a long time and in turn has turned you into a more attacking force , you can see this as Kuyt is playing more forward as a result... Zaki... well he's brilliant has won them points when without him they could well be down the bottom and in trouble... Nasri.. just fantastic, so confident on the ball and has ball skills and attributes galore... and he's scored a few as well... If pushed I would vote B A then C.. if Riera scored goals he could/ would be higher.