As primes go I would choose the 35 mm 1.4L for what you describe.
it is wide enough for landscapes, for portraits it is great for capturing person at location type shots. Use it at f2.0 or wider it can produce really cool separation.
50mm results are more plain IMO as the FOV is close to what the human eye sees.
Of the two focal lengths I prefer 35mm.

The 24-70 II is as good as it gets when it comes to Canon wide zooms.
The IQ of the 35mm and the Zoom are about the same at 35mm.
The zoom has more distortion and vignetting but if you are using LR5 you just select lens correction when you process and it magically disappears.
So the only reason to buy the prime, and for me this is an important one, is the magic the 35mm 1.4L can create at f/1.8 to f/2.0.
At f/14 the IQ is not so good. When picking the prime the IQ wide open is the most important.
Low light for me is only a minor consideration as the zoom is super sharp wide open. You only gain a bit over a stop of light, before someone jumps on the math of the statement I do not consider the IQ of the prime usable at 1.4.