The 35 f/2 is a great little lens. I shot it nearly exclusively for a year, and sold it for the 35L. The build of the f/2 isn't that bad. It is the same practically as the 50 1.8 MK1, and better than the 50 mk2 by a long shot. It's a litlle noisy, but I never really had an issue with it.
since you are buying for a 400D, the 35 is not a "wide angle" for you and the 50 is a portrait length lens. The difference between f1.4 and f1.8 is negligible for DOF, better to go longer for outdoors. Frankly, the only reason I see to buy the 50/1.4 over the 50/1.8 is if you think quieter focusing of USM is needed (never mind that the shutter is going to be way louder than the non-USM motor in the 50/1.8) or if you prefer the *look* of the 50/1.4 (after shooting both for years, I realized that more often than not *I* prefer the look from the 50/1.8).
I think that most people who claim that the 1.4 is "much better" than the 1.8 comes from people who started out new to photography with a 1.8 and then as they were getting better "upgraded" to the 1.4... and then don't realize that most of the difference came from them gaining some more experience.
