Originally Posted by stevebrot 
Since when is the purchase of an "off-brand", "settling"? My main consideration for a Pentax-M 135/3.5 over the other alternatives would be size, weight, and the SMC coating. Performance compared to a Tamron, Rikenon, or Vivitar of similar vintage would be equivalent with a bit of a nod given to the generally faster maximum apertures on those "off-brand" options.
Steve
True enough. Different priorities for different situations. I own 4 Pentax 135s..... M42 SMC 135/2.5 & SMC 3.5, K-Mount 135/3.5 (52mm filter) & the aforementioned M135. Although a very good lens, my M offers me less quality than my other 135s. I do, however, use it often when I'm looking to travel as light as possible, with my "newsman's combo", consisting of the M135, an M50/1.7 (again, a fine lens, but of lesser quality than other larger Pentax 50's I own), and a 28mm/3.5M (another fine performer, but of lesser quality than my M42 SMC 28/3.5 & Pentax 28mm 52mm filtered lens). Along with these small, light lenses, I use an *ist DS body..... quite a small, light combo that is tightly fitted into a surprisingly small case. But if size & weight is not an issue, the other lenses you mentioned would certainly suffice.