Samsung 45mm vs Rokinon 85mm?

So there are a few thing to consider in this area. 
I like to think about things in Full Frame only because so many people I know and learn from use full frame and that is just how I think. 
the 45mm is just shy of 70mm and the 85mm is about 130mm. 
For portraiture 85mm is your start point for tight portraits. You wouldn't normally really use a 70mm unless you had no other choice. 
That being said a lot of those rules are BS to some extent here are two photos outtakes from a shoot a did a while back, one taken at 60mm one at 30mm (the 30mm I forgot to dial down the lights but liked the pose so I played with it.)

60mm on the left - 30mm on the right.  (outtakes don't judge me on these )

The 30mm is in tight neither photo is cropped or corrected in post. The Poses are similar, and they are filling the frame in a similar manner. Normal rules suggest a 50mm (ff) vs a 90mm (ff) should result in a noticeable distortion in the 50mm.

Because Samsung lens auto correct some of that distortion in camera it isn't such a big deal.

So from that point of view either lens will do the trick.

Both lens' are sharp (generally)

The 85mm is on my list because I like shooting further back from my subjects. To me that is what you should consider, do you like to be closer or further back? Also how wide do you want to see? How are you are manual focusing, will you be on a tripod most of the time.

Those are the questions to ask. Beyond that both lens are supposed to be very good.