Its better to find a network that has better coverage in your area.
However, for people having low coverage.
1. Use of aftermarket phone cases for protection weakens the signal strength (slightly, but it does). If someone is laughing at me. They can check themselves with the method attached in link. It is more noticeable in low coverage areas.
https://www.pakwheels.com/forums/showthread.php?p=4958537
Covering the phone antenna also weakens the signal strength. So it's better to hold the phone the right way, especially when signals are low. Main antenna is ALWAYS at the bottom in all phones.

I never paid too much attention on signal strength in different phones, but Microsoft Lumia, Motorola, iPhone 6 and 6S are better at signal reception, that's what I noticed.
Getting US carrier phones will get you in more trouble in low coverage areas.