Hello piergiuseppe.tundo@mermecgroup.com,
This is depends very much on the application you want to develop. All those examples are using the NFC Reader Library. But every has a dedicated purpose to showcase different functionality.
If you want a NFC Forum compliant reader to communicate with tags as well as with mobile phones you should have a look at the example 'NfcrdlibEx3_NFCForum', but if you want to use your reader as a PC/SC CCID device it will be an easier start by looking at 'PN7462AU_ex_phExNFCCcid'.
In general examples starting with 'PN7462AU' are dedicated and only available for the PN7462. On the other hand examples starting with 'NfcrdlibEx3' are independent of the reader chip (as long as the functionality is supported) and can be used with various NXP reader chips (CLRC663, PN5180, PN7462, etc...).
A good start to get familiar with the use of the NFC Reader Library might be the basic discovery loop example. As soon as you know what your host interface should be (USB, VCOM, UART, SPI, ....) you can look into one of those examples as well. Most probably your application in the end will use snippets from more than one example.
I hope this was helpful. Do not hesitate to ask if anything has been left unanswered :smileyhappy:
Best regards,
Alex