Originally posted by blende8 My recommendation after 30 years of photographing and dozens of lenses:
Whenever there is an alternative from Pentax, take it.
I would most definately say NOT to ever use such a rule for decisionmaking.
Such a rule would result in people choosing the Pentax 75-300 over the Sigma and Tamron variants, which is most definately not a wise choice. Every review I have heard of the Pentax 75-300 has been very negative. The Tamron and Sigma variants are by no means perfect and both have known issues, but the general opinion of the Pentax version seems to be "awful in every aspect".