All three of these methods can provide you with straight hair; the only difference is in intensity and timeline. Most of the pros and cons that you have to face are present in either of the three methods.
Simply put, Hair Straightening is the process of subjecting your hair to heat with the help of flat iron to make it appear straight. This method only makes your hair straight temporarily, and the next time you wash, your hair will get back to its original position.
Hair Relaxing is a more in-depth method to achieve straight hair. In this process, the bonds in your hair that give it texture and shape are broken down with the help of chemicals. It permanently straightens the hair strands it is applied to. A neutralizer is then used to stop the chemical process, and your hair is conditioned and styled.
Hair Rebonding is the process of putting both the methods above together to provide a final, smoother, heat-sealed result. Instead of the use of heat to style, hair rebonding process uses keratin treatment to give you a longest-lasting, shiniest hair possible. Using this method will make your hair look healthier compared to when you use any of the other two techniques.
Since hair rebonding combines all the processes, it tends to provide everything that you might be looking out of hair treatment. With Hair Rebonding, you get straightened, healthy hair that does not go back to its original condition.