C300 is a dog. C250 is nearly as fast (feels faster IMO, perhaps that is just the turbo) and gets much best gas mileage out of it's turbo 4-banger than the NA V6 in the 300. Plus they don't make C300's anymore, the styling differences in the C250 are more preferable as well - especially the coupe with the two-tone interior & sport steering wheel with thumb-rests.
We were turning in our C350 lease and I was comparing the new (at the time) C250 vs. pre-owned C300 vs. the new C350. Went with the 335i because after I test drove it, the CXXX's felt like I was driving a Camry.
2008 e90 335i