first, which carrier? between verizon and ATT (and the others that use either verizon or ATT signalling) we often find one or the other will give a good signal, but not both when we are in remote locations. easiest solution is if one gives a good signal use that carrier. That's why our cell phones are Verizon and our car is on ATT.
Second, boosters require a minimum signal level to be able to get you a useable signal. Signal level needs to be around -140/150db or better for a booster to work. -140db with a booster will get you a signal around -110db which is adequate for voice and text. -140db will generally not give you a useable signal w/o a booster.
And you may find a booster will give you good voice but not data. In one spot we visit signal level is around -130db, booster gets it to -90db or so, but signal is only voice (1x) no data other than messaging.
And "bars" is generally not a good indicator of actual signal strength. use a app that gives you actual signal strength for voice and data channels.
We have a weboost system that I can use with either an omnidirectional antenna or a directional yagi. Does it work everywhere? NOPE. Does it give me a useable voice/text signal in very marginal conditions or when there is no service w/o a booster? YES in many cases, but not all.
Finally I've found that if I need a booster for data, even with a booster data rate is generally much slower than areas that don't need a booster.