When I used to configure IPsec VPN with ASA I usually had the PRF set to the same value as integrity (or authentication), because most other software used this setting and often it couldn't be changed.
If you're in doubt, you can capture the IKE_SA_INIT exchange and analyze it with wireshark (this is not encrypted). You'll find the values that are used by ...
These are the default settings that appear when you go through setting up a site to site via VPN Wizard.
These are the default settings that appear when you go through setting up a site to site VPN Manually.