Upload & Sell: On
This is such a difficult question!
I finally voted. No surprise, I chose the 35L. For my style of shooting, I prefer to have AF as an option. This lens is in need of a redo, and would be even better with IS added.
I don't like an excessively bulky or expensive prime lens -- I'm always worrying about the lens, not getting the shot. This was my problem with the Zeiss ZE 21/2.8 -- always treating it gingerly, so would leave it home and use something else. Once I found I could easily get by without it (same for the ZE 35/2, after buying the Samyang), it was just a small bank account waiting to be cashed in. That, and the various lens aberrations, are what keep me from pursuing Zeiss lenses, at least for the time being.
But if cost, bulk, lack of AF, and Zeiss-style image idiosyncrasies aren't an issue, the ZE 35/1.4 is the best lens of those listed. Too many "ifs" for me at this time.
Agreeing with both Kevin (Samyang 35/1.4) and Dan (EF 35/2), I can get by well enough for now owning these two lenses, plus the couple "L" zooms that have 35mm included.
The 40/2.8 STM is a pretty awesome lens. Mine is in to Canon for adjustment for unflat focus plane (weak right side and field curvature). But otherwise, it has great sharpness and very nice OOF edges wide open, if you can live with 2.8.