Coros vs Garmin heart rate straps. Which one to trust?

I previously tested the Coros optical arm heart rate sensor against the Garmin Run chest strap.
Recently I've suspected the Coros strap was giving false readings so I compared the two again with some interesting results.
NOTE - I am testing the Coros Optical arm band and the Garmin Run chest strap NOT the optical sensors on the back of the watches!

[@georgevadnais3516]

You place the coros where coros tell you without looking where are you'r veines. I wear mine inside my forearm where i have big veines and it’s bether .

[@fellrunningguide]

Yes I wear it on the upper arm as recommended by Coros. It doesn't fit as well on my forearm.

[@georgevadnais3516]

@@fellrunningguide look for the best veine that you can see, put it on an make a test. ((( If you want ))) for me insiste my forearm, close to my elbow = sweet spot.