I know very little about antennas, and I'm trying to improve the reception/transmission of a device that uses 4G technology to connect to the cell network. I have noticed that some antennas perform a little better than others, but I have no idea as to how to actually measure their performance. Is there affordable equipment out there that I could use for this purpose? ... something that I could plug the antenna to be tested to, and then measure its performance as I change its place and orientation? ... @nsaspook

For instance, would an antenna such as this:

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Perform better than an antenna like this one?:

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Define affordable. The cheap NanoVNA devices will work as a relative measurement.

In general, with nothing else changing, if the signal is marginal, another few db of directional gain from directivity won't make a big difference.

Shown are different antenna design types for multi-band capabilities. If you're only going to use one band then an antenna designed for that band will generally have higher efficiency.
Try to find antennas that have actual data for a comparison.

https://antennatestlab.com/antenna-education-tutorials/is-more-antenna-gain-better