"Mt." is a more common abbreviation, especially in the United States. It is often used in place of the full word "mountain" in place names, such as Mt. Everest, Mt. Hood, or Mt. Kilimanjaro.
"Mount" is a less common abbreviation, but it is sometimes used in more formal or literary contexts. It is also more likely to be used in the United Kingdom and other parts of the world outside the United States. For example, you might see the term "Mount Everest" used in a British newspaper or magazine, but "Mt. Everest" would be more common in an American publication.
In general, the choice between "Mt." and "Mount" is a matter of personal preference. However, there are some cases where one abbreviation is more appropriate than the other. For example, if you are writing a formal document or essay, it is best to use "Mount." If you are writing a casual email or blog post, "Mt." is perfectly acceptable.
Ultimately, the most important thing is to be consistent with your usage. If you start using "Mt." in some place names and "Mount" in others, your readers may become confused. So pick one abbreviation and stick with it.