Call me a BMW loyalist, because some Porsches and Ferraris are too expensive for me.
Go with the 335i.
One of the leading german carmags Auto Motor und Sport tested the Sportline 335i A vs a C350. The C350 still is pretty good but the 335i won.
0-100kmh(62mph) did the Benz in 5.5 seconds. The 335i did it in
5.1seconds
0-130kmh(81mph): 8.1 seconds. C350:9.0 seconds. F30 328iA :9.9 seconds. Who said that there's no subsitute for cubic inches LOL. At this point he/she's right.
Brakingdistance 100kmh-0(cold) :35.6m (warm): 36.1.
The slalom and wedeltest/handling the 335i also is some kmh faster through them than the Benz.
At the end of the day ams finds the C350 the 'more cool' car(...) and the 335i the more agile/sporty one, but a bit bland by the looks of it....