I don't have the K85/1.8, but I do have the Takumar 85/1.9 and M85/2.
The M85/2 is unique.
About as small as a 50/1.4 prime, contrasty and very bold drawing of subject.
Very sharp if focus is correct and also stopped down.
Its main weakness is CA and flare in harsh conditions.
I'd take this out more often than the FA*85 and Takumar because of size alone (not to mention its bold drawing style)
The Takumar 85/1.9 is an excellent lens.
Well built, a joy to focus with its smooth focusing ring.
To me, its rendering is 'pre-SMC'.
A gentler drawing style and less contrasty (though still nice colors bit seemingly on a lighter palette )
AFAIK, the Takumar 85/1.8 will be as well built and said to be better.
The K85 is sought after and usually costs more than the 85/1.9 and the M85/2.
So I'd suggest getting the K85 since its the same price.
But the reality is that everyone should have more than one 85mm
With the M85/2
With the Takumar 85/1.9 (but sample unfair advantage to it as its on FF)