Google pay activates automatically when you bring it close to a reader. From the NFC settings I've chosen Samsung pay as the default for this does this too but it does not. The reason I still prefer Samsung pay is that I can disable it for public transport.
Google pay is so much better than Samsung pay for this very reason alone!
HHowever, I live in Stockholm and buy monthly public transport tickets from the SL app. The ticket appears as a QR code. The QR code scanner is very close to the NFC reader. So if I use Google pay and set it to work automatically, it gets activated by the reader and I effectively get charged twice. Google pay doesn't have the option to turn off use on public transport, unlike Samsung pay. If I simply turn Tap to pay off then Samsung pay is easier to use. That's why I'm hoping Samsung would do this.