How to select Processor / Microcontroller for your design

1) Specify the basics
For example: You want a cheap ARM processor, at least 300MHz with DDR3 interface

2) Answer this question: Which is the most unusual peripheral I need?
For example: HDMI interface

3) Go to a supplier website and do the search
For example: http://www.digikey.com -> Product Index > Integrated Circuits (ICs) > Embedded – Microcontrollers

4) Select the unusual peripheral: Peripherals -> HDMI

5) Order Ascending by price for 1000 pieces

If you don’t have any special peripheral, search for:
Processor core: ARM
Speed: at least 300MHz
Industrial temperature: at least -40C

6) Check datasheet & manufacturer website

7) Select the processor most suitable for your application.

Be careful about

In stock checkbox – this can eliminate the cheapest variants from the list, so the results will not be accurate. On the other site, be sure, you can buy the component you finally choose.
Category selection e.g. Processor / Microcontroller. Suppliers sometimes mix these chips together, look in both categories.
Hardware development support – be sure, the selected chip has free reference schematics with PCB and available development kits in reasonable price
Software support – be sure, the selected chip has a good software support with code examples. Additional software development can cause delays or increase cost significantly.
Good documentation is advantage.
Community support is plus.