I have the samyang 35mm 1.4, and also used to have a canon 50mm 1.4 alongside it. I found that during a portrait session 2/3 of my photos came from the 35mm rather than the 50. I just found that I preferred the 35mm focal length on crop over the 50 1.4. In my opinion the image quality and sharpness was better, as well as bokeh. Also, because the Samyang is manual focus (I dont know if you knew that...) i found myself getting more exact focus when focusing in live view with digital zoom (the best method I've learned to use the lens).
The canon 50 1.4's build quality isn't the best either - the focus ring tends to jam quite easily even if you are careful as I have learned (twice, unfortunately).
So, I kept the samyang and downgraded my 50 to a 1.8, but still prefer the 35mm 1.4 for it's IQ and focal length. Once you get used to manual focusing with it in live view and you are nailing focus it is an incredible, incredible lens, on par with the 35L on image quality through all the reviews and comparisons I've seen (and when I've used the 35L the only thing I found noticably better was the auto focus).
I have also used the 85 1.8 before, and it is freaking awesome for portraits. I think a Samyang 35 1.4 paired with the 85 1.8 would be ideal, maybe a 50 1.8 in there too as all intro low-cost lenses.
If you have to choose one think about the focal length you prefer using based on the gear you currently have... but honestly I'd throw the 85 1.8 in instead of the 50 1.4 due to build and my personal experience...
The only thing that holds me back from fully recommending the Samyang is its lack of autofocus. Otherwise, I absolutely love it.