The best boxer pound for pound, in my opinion is Andre Ward.
Most people still give Floyd Mayweather the number one spot simply because after Manny fell away nobody has beaten Floyd. The fact remains that since Mayweather left the 130lbs division many years ago, he has avoided most of the truly interesting and career defining fights that the hardcore fans want to see. His resume of the past few years has been made up of fighters that you would give no more than a 25% chance of beating him. There was a fight with future Hall of Fame fighter Miguel Cotto but that came five years after it was an interesting fight, it was a typical piece of Mayweather matchmaking, catch him when he is cold.
Andre Ward is quite a boring character, a devoutly religious man who calls himself 'Son of God'?! He has faced the best fighters in and around his division in recent years and has not even been in a close fight. In fact, he has barely lost a round. He doesn't have a big punch but he has just about everything else a fighter could desire: speed of hand and foot, a good chin, tactical nous and extreme dedication to his craft. What impresses me most about him is that he knows how to work effectively for part of the round to score points, but he also knows how to completely nullify his opponent for the rest of the round, he steals every second of the round. He is prone to using the dark arts and criticised for not leaving his home town very often but I can't see anyone who, if all fighters were equal in weight, could beat him.