Actually i think Kompany is a better defender than both Puyol and Pique....especially Pique.
They both play in a team who absolutely dominate possession. They are rarely on the back foot, and at the Nou Camp, most opposing teams don't often make much impact in the final third as they simply don't have the ambition to get bodies up field quick enough. Barca press very well as a unit and usually win the ball back somewhere around the half way line.
Pique has good technical ability and he is big and fairly strong. However, don't let his technical ability fool you into thinking he is the best defender in the world, because in reality he's nowhere near. His decision making is very erratic and his concentration levels aren't the greatest. His positioning can be a bit off at times and he can also be a little rash. Sometimes he just does things which can oddly be described as 'odd'.
Commentators talk about how much he's improved since his United days, but i just don't see it. He does things that make you say 'he's a good player' but that doesn't mean he is the best at what he should be doing, which is defending. A pinpoint 40 yard pass is great when a defender can confidently pull it off and he can. A shimmy to lose the attentions of an attacker can also look great. But it's the bread and butter stuff which he sometimes struggles with, and that's why i would much prefer to have Kompany playing for us than Pique.