Recommendation for lens

If you find a Tessar/Xenar it's a very sharp and contrasty lens. As you are using a 6x9 camera you will be in the sweet spot of the lens, where the Tessar is at its best.
Else, any of the big four (Schneider, Rodenstock, Fuji and Nikkor) makes good lenses. A modern multi-coated plastmat from any of these will serve you good.
The Sironar-N is the "common" plasmat, which is on par with the other brands. In the "S" series, more expensive glass is used, which enables a construction with a few more degrees coverage. The S-series usually performs a little bit better, but the question is if anyone will notice. You decide if you will get better pictures with a marginally better lens. (I'm not saying that I don't want a Sironar-S, cause I do, but I found myself a Symmar-S and used the money I saved on lots of film instead. The Symmar-S performs very good in my mind, so I'm satisfied.)

//Björn