I am not really certain how people will react to this type of thread, but uh... Curiosity abounds as to what opinions this might draw out.
If we take a gunbreaker and a dark knight as we understand them to function in lore and place them in a 1v1 confrontation, which one is more likely to come out on top? We'll assume luck to play no part, equal skill in their respective disciplines and equipment between combatants, and a completely open battlefield.
I personally am a bit stumped by this question. I feel like a dark knight might have the edge in raw power, but my personal familiarity with guns and explosives makes it really difficult for me to make that assessment conclusively. I do feel that a gunbreaker would probably be much more agile than a dark knight.