I have a 2012 (8600 miles) and as far as I know, the only differences for 2013 are the media interface, and some knobs as well as some interior tweaks. I have a Sport Sedan, so you will have a suspension that's a bit stiffer and some aesthetic differences. Like the other users said, the C250 has real nice passing power, but is still very slow. Also, when I test drove the 328i and the A4, I felt like the Benz felt a lot more nimble than the other two cars. In the city, I get about 20-22 MPG and on the highway, it's not difficult to get 30+. As far as city MPG, it may be my style of driving as she's always in "S", it's the only way to feel some real power haha.
Likes: Handling, mid range power, Mercedes Benz quality, updated interior (when compared to the Audi and BMW interior, the Benz seems newer while the other two seem a bit outdated)
Dislikes: Somewhat slow, noticeable turbo-lag if punched off the line. In addition, I feel like there is not that much legroom in the back seats. (5'9" skinny ass dude)
There are also a bunch of subjective factors that you might wanna consider, such as looks. Some people don't like the 2012+ facelift, some do. All in all, I am very pleased with my choice (although not a '13, like yours, close enough, right?) and wouldn't trade it in for anything else.
Good luck with your purchase!!