RB67 lenses

What are the differences between the 90 3.8 and the 90 3.5? the difference in aperture is minimal and the 3.8 are cheaper. Are they also worse in any other way?

What are the best out of the difference flavors of lenses like the C lenses and so on? I'm more concerned with reliability than with ultimate coating or anything.

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...and there are many other threads on this subject.

For colour work, you will probably prefer the newest KL lenses, which have better colour correction and coatings. There are many arguments back and forth regarding which are more reliable (because the newer lenses have shutters that some regard as less reliable), but... it's a wash, in my opinion. If you buy an older lens then you get with it that lens' usage history too. I advise to buy the newest and best condition lens you can afford; the price differences tend to be so minor now.