Those are two different ideas for a ‘grand unified theory’ of how we can combine different parts of physics to explain the world. As far as I know no one has come up with an answer about which one of those is the better theory, and there definitely isn’t a good solution to the grand unified theory yet. Thanasis can probably tell you more though!
Since the middle of the 1900s scientists have at their disposal two very successful theories: Quantum mechanics, which described how matter behaves on an atomic scale and the general theory of relativity which describe how space and time and not two separate entities but a single variable, spacetime
The problem here now is that these two theories don’t blend very well with each other and require some other theory in order to have a so-called “Theory of Everything”.
String theory and loop theory are two contenders for unifying quantum mechanics and the general theory of relativity. While both of them are developed theoretically, scientists need to do experiments in order to confirm or reject them – some of them are already ongoing.