It's never a bad idea to be all around, that way you're never at a huge disadvantage against anyone. I use shooters, and move around A LOT and use inefficient weapons, so I focused on speed and ink efficiency. I use swim and run speed, and ink efficiency and ink regeneration, and that set matches my play style. So if your play style works well with one ability, focus on that. Just don't leave any glaring weaknesses in your set. I replaced my weaknesses, and then added speed, making it very hard to deal with me. That set would not work for snipers though. It's all about how you play.