gps speed sensor?

If you're asking about an actual in dash gps speedo, I'm running an autometer #3982 I'm happy with. The phone apps etc are hit and miss for sure.
The autometer one I run has a wired sending unit that ends with a small sensor, about the size of a couple quarters stacked. It's magnetized, I stuck it to the dash. Even entirely under the cloth dash cover it picks up signal and reads accurate. In longer tunnels and some really enclosed/underground parking garages it will lose signal, but it comes back almost instantly when the car gets close to the sky/open air. Simple install, effectively just an accurate speedo that I can swap rear gears and tire sizes without any hassles. I'd buy it over a mechanical one again in a blink.