What a hard question! On my first play through, I used Gunslinger and Swordmaster, and on the second run, I also started to use Trickster (it helps a lot when fighting against Vergil, haha). So maybe one of those would be the most useful style to me... but which one? I don't know. But I know it that if I mastered Royal Guard, it would be great. I've tried it a bit and succeeded at blocking something, but it's still a bit hazy part to me as to how exactly I did it, lol.