This seems to be a popular subject. My history with 135s goes back more than half a century. After my standard lens in 1971, my next lens, in 1972, was a 28. In 1973 I finally got a 135. It was a Vivitar f/2.8 (28XXX...) model and it served me very well. My only complaint about it was that it didn't focus very close. I would later trade it toward a 135/3.2 Konica Hexanon, which as has been mentioned, focused down to three feet. If my memory on this is correct, the 135/2.3 Vivitar Series 1 which I later got, also focused down to three feet. These two lenses were useful for portraits. The 135s which got down to five or more feet were not so useful for portraits, especially of young people. I think my favorite 135 must be the Vivitar f/2.8 Closse Focusing. It gets down to 1:2 and has always given me good results. I think I have it in every mount it was made for. It does not seem to have been made in Yashica/Contax mount. Some of my best portraits have been made with it. For outdoor medium distance shooting I prefer a 135 to a 90-105. I think it separates the subject better.
Some of my other favorite 135s: Canon FL 135/2.5, Canon FD 135/2.5, Nikor QC or 'K' 135/2.8, Sigma 135/2.8 Pantel, Konica Hexanon 135/2.5, SMC Pentax 135/3.5.