Will not and Won't

"will not" and "won't" mean the same thing, as you know.
"will not" is used in formal writing, but it can be used in conversation, too.
"won't" is used more often in conversation, but it can be used in informal writing, too.

"will not" can be used in conversation for emphasis.

My recommendation:

If you are learning English primarily for conversation, use "won't" most of the time.
If you are learning English only to do formal writing, use "will not" all of the time.

Others may have different opinions on this point.

Many thanks for your advice, very clear and useful.