Which one: Nikon 50mm f/1.8 or f/1.4, or 85mm f/1.8 or f/1.4?

I'm a beginner photographer with a Nikon D5100, will these lens be compatible with my camera? I'm interested in portraits, what lens performs better with producing bokeh, sharpness, etc? Also, what one is cheaper? For more advanced photographers, what one do you recommend that I buy?

Checked the prices on any of those lenses, suggest you do then come back to earth. You said you were a beginner but want professional equipment…

If you know that you are going to do enough portraits for it to be worthwhile, 85mm is a better focal length than 50mm. 50mm is the 135 equivalent of 75mm, and in the 135 film era, no one was selling a 75mm portrait lens.
You might get more value from a 60mm AF-S macro, which could do macro and portraits.

If you have money burning a hole in your pocket, have you already bought a GOOD tripod and an external flash?