For me, in terms of meaning there is no difference at all. I would say "making" is probably more usual in speech and in writing.

"To make a best friend is not easy" doesn't sound as natural, especially in casual speech. "To make" is the infinitive and does express the same idea as "making", but most native speakers would use "making" in this sentence, and in any similar structure. Another example: "My least favorite task is washing the car." vs. "My least favorite task is to wash the car." We often won't naturally use the infinitive, but the two forms carry the same meaning.