The most powerful jedi/sith ever to have existed?

You going need to read the books and comics to find that out.I know Han solo in the SW books had a girl who turned into a jedi and the jedis gave her a purple lightsaber(purple one is only given to special jedis).Also does it seems the more newer something star wars is the more powerful the characters seem to be? look at obi one in episode 4,he barly moves and episode 3 one jumps like place to place over lava and almost takes out vader.