I'm thinking about it, and I'm not sure. I will try to explain this simply. I like to take my time aligning sprites. They are important to make the character look smooth and realistic. I like to take my time making FX for the moves. The sounds and lights, air, and dust make the character seem like he affects his environment. I like to give my characters colors that are bright, but appropriate shades. Palettes are important. I try to consider damage and combos because that makes a character more fun and usable. If a character is difficult or frustrating to use, that makes the game less fun.
You can put a lot of work into something and nobody will notice it. It won't look like a problem. That is what you want to do. If you rush something, somebody will ALWAYS notice. It won't look right to their eyes. It won't sound right to their ears. They will think something is missing because they understand how THEY affect their environment. If you see a character in a weird pose, you will notice. Would you ever stand the way they are standing? Can people move the way they are moving? How does the human skeleton move? Yes, they are super heroes, but Superman's skeleton still moves like yours.
My point is that everything is complex if you think about it. You can always expand on a certain aspect. Details! To answer your question, for me, the quickest is aligning sprites, and that is still a lot of work.
by 
