Most high performance modern GPS devices are able to receive signals from the 4 major Satellite navigation providers.
They are the orignal "GPS" owned by the US, GLONASS owned by Russia, Galileo owned by Europe and Beidou owned by China.
They are all similarly accurate. The biggest gains in accuracy come from using dual frequencies from the same provider.
This is why the Garmin 255 is the watch of choice, it is the cheapest watch that can simultaneously use multiple systems and dual frequencies.
Next big improvement to expect are the LEO GPS systems, where LEO stands for Low Earth Orbit Satellites. Existing GPS satellites are in the MEO (Medium Earth Orbit), around 20.000 km above the Earth. LEO is more 100 km - 400 km above the Earth. Signals should be 100* stronger, and precision (without RTK) in the cm range. I guess Doppler speed will also more accurate. To cover the complete Earth, some 100 satellites are necessary, as each satellite has a much smaller coverage.
www.esa.int/Applications/Satellite_navigation/ESA_plans_for_low-orbiting_navigation_satellites
