Before you switch carriers, see if any of your friends with different carriers can go with you to wherever your phone doesn't work.
See if their phones work.
Then see who has the best signal.
I only say this because there are still some areas that have virtually no cellular coverage, and in that case you need something else.
For a friend of mine, I went to his home with two different phones from two different carriers.
Neither one worked well at his house.
But he does have good Wi-Fi, so I helped him set up a VoIP app on his phone to use his Wi-Fi instead of cellular when he is at home.