Which is better is a question that often comes up. It is similar to what is the better choice but it can have more specific meanings. Both are grammatically correct, but they do differ in the use of a subject and predicate.
Both is used to describe something that has a higher value than another item or condition. For example, you might say that a hot shower is better than a cold one because the warm water will help relax your muscles. It is also possible to say that a good student is better than an average student because the good student will have a greater chance of getting a scholarship or finding a job.
The word better is a comparative adjective, meaning that it has more goodness than something else and less goodness than the best. For example, a bronze medal is good but a gold one is better because it has more goodness than the bronze medal. You might also be able to say that someone is better off than others because they have more wisdom, wealth, or happiness.
Which is better can be used in many different situations because it can compare two or more things that you are considering. The question is a great way to ask for someone's opinion and will give them an opportunity to choose which option they prefer. You might also choose to write or say which is better because it has a more formal tone and could be used in a professional context.