Warning. I am the author of pigpio so will be biased.
You might get a taste by looking at elinux.
RPi.GPIO was the first and is the most popular. It will be the one you most often see examples for.
RPIO builds upon RPi.GPIO (it is meant to be a plug in replacement) and adds some capabilities. In particular it adds hardware timed PWM suitable for LEDs and servos and hardware timed pulse chains. RPi.GPIO only provides software PWM which gives visible glitches in LEDs and is said to shorten the life of servos. As mentioned in RPIO github repo:
This repository is not actively maintained anymore!
wiringPi Python is a port of much of wiringPi's C functionality to Python. I haven't used it and don't know much about it.
pigpio Python is a port of pigpio's C functionality to Python. Like RPIO.GPIO it provides hardware timed PWM for LEDs and servos, and hardware timed pulse chains. One unique feature of pigpio is it times GPIO events at source so for any timing purpose pigpio is likely to be the most accurate. pigpio can run on a networked PC (Windows, Mac, Linux) to control a remote Pi.
gpiozero is a simplifying wrapper around pretty much any of the above libraries. It is in effect a front end which tries to remove the user as much as possible from the underlying implementation details. gpiozero (I think) is the Foundation recommended Python start point. gpiozero can (I think) run on a networked PC (Windows, Mac, Linux) to control a remote Pi if pigpio is the backend.
Warning, ask 10 other people and they will have 10 different views. All the libraries have their uses. They are all tools. Which is best for you depends on what sort of workman you are.