I recently took a 35 f2 and a 35 f3.5 on a trip.
The f2 with its built in radioactive yellow filter is superb even in backlight. The f3.5 was multicoated and even at f8 is dreadful in the corners.
There are two versions of the f2 -one uses a 58mm filter. There also exists a 35 f2.3 which I really haven't tested much. It seems ok.