Which C Class for 7k?

[AudiSport]

Hi guys, after a string of Audis and BMWs I fancy a change, and have been looking at Merc C Class Saloons for around 7k, however I would really appreciate some input on what options to look out for, and what the real world difference is between the C220, 280 and 350? I'm after something that will feel sporty, with sensible mileage and either diesel or petrol. I do around 10k a year miles, so I know petrol makes more sense, although I do enjoy the low down torque of the diesels.

Thanks in advance for any input.