Previously I noted the importance of knowing the applied cost of a connector.  Here are the basic questions I start with when helping to design in a product:

• Not the number of pins, but the number and type.  Signal speed and maximum power
• Amperes at what temperature?  Ambient temperature and cooling are key
• What is the connector orientation?  Are we talking mating direction or position relative to the board?
• How is the connector going to be applied to the board?  Pick-and-place, hand placing, or press in?
• Tin or gold plating?  What is truly needed?  If 50 milliohms with less than 50 contacts and less than 50 cycles, tin may do the job

Given the opportunity, here are my additional questions:

• Application:  Board-to-Board, Wire-to-Board, I/O, or Backplane
• Any space limitations?
• Number of signals, speed, and single ended or differential pairs?
• How many grounds for signals?
• How much power?  What about power returns?
• Any higher voltages (> 50V DC)
• On the PCB (SMT) or through the PCB (wave solder or pin-in-paste)?
• Lead-free reflow processes require reflow temperatures at +260°C, Lead free wave solder processes need +300°C underneath the PCB
• Height constraints?  We need to factor in any pick-and-place processes
• Are there any wire size restrictions when using wires or cables?  Can I solder, crimp, or IDT?
• Environmental restrictions and norms such as UL, glow wire, or halogen-free?
• Preference for any contact spacing due to mechanical tolerances?
• What is the timeline for samples, ramp up, and volume production?

As soon as all these questions are answered, I have a very clear view of what is needed.  I can now search my favorite web site (molex.com ) for the best product for the application.  Always considering that the application is not where the product ends up, but how the product is applied!