But some phones do have better reception than others, and if you are in an area of poor coverage this may matter.
Unfortunately reviews rarely test this, so unless you have someone with experience of 2 handsets who can compare them its hard to find out. Also the test is whether it can use the signal and not how many bars it shows (the manufacturer chooses how many bars it shows for what signal level, and can change that to look better without improving reception at all), which means you have to deliberately test it in fringe areas.
I know from people who have done such tests that the HTC U11 has better reception than the HTC 10, but don't know about S8 or G6.