It depends on what you do. If you do street photography at evening/night time then 50mm F1.4 on full frame camera is your thing. If you engage in portrait photography then 85mm F1.8 on full frame is irreplaceable.
If we are talking about Canon EF lenses it has to be said that Canon EF 85mm f/1.8 is a gem of a lens while Canon EF 50mm f/1.4 is of inconsistent quality.