Best GPS setting for open water swimming

Try it and see. GPS settings appear to be location dependent. Mine’s always been on GPS+GLONASS and that’s worked well enough.

I am in Canada and GPS only fluctuates lots. Sometimes the watch lost the track and instead of  showing 3000k it shows 1400k with GPS only mode, I find more accurate the GPS+glonass or + galileo. Ultratac not recommended for open water. Some people attach their watch to their floaty bag so it is more accurate, others like me just keep it on the wrist but the stats are not the best. 

Note that GPS for breaststroke-style doesn't work at all because watch immersed all the time. It works for freestyle only. It means that GPS should catch a signal during above-water phase. I noted that it isn't happen with every stroke because my track looks too smooth. I also noticed that the watch is aware about that and its algorithm tries to approximate the distance based on strokes and GPS signal, when available

Im in Turkey and gps only works better than the other options. I do *** stroke so its not too accurate, ive decided to save and then restart recording my open water swim after reaching each of my destinations. While i do know my across to be 300 meters, i rely on garmin (swim 2) to tell me my outward swim meters, which is usually around 1.20. I do the math anyways and know how much i swam but i really wish my watch did too. 

I am very happy with my old Fenix 5x Plus even in open water swimming.
The day before yesterday I swam over 4 km and in the end the difference with the Epix Pro was only 20 meters.
F5x+: GPS+Galileo smart track
Epix Pro: GNSS enabled 1 second logging
Considering the generation gap, absolutely not bad.
Nothing to do with the OWS mileage problems I had with the Fenix 6x pro which recorded 15% less!