In my opinion, Breaking Bad is far superior.
When Weeds came out, I had to watch it, because - weed n growing and shit. It started out pretty good and even occasionally touched upon personal experiences. But somewhere around or after season 3 it really went off the rails. The plot was pretty clearly out of control and started to devolve into Nancy's love life and dozens of shitty sub-plots. But we kept watching anyway with increasing impatience. But you could not really ignore the fact that there wasn't a single character that you gave a crap about anymore.
By the last season - which by the way was an unfocused horror driven my the need for actor's agents to claw one last sub-plot out of the script regardless of the impact on the story - I did not care. In fact, minutes into the final episode, we turned it off. We no longer cared what happened to Nancy Botwin.
Breaking Bad? Totally the opposite. Every plot added to the story. Characters were focused and meaningful. You cared about every one of them despite the conflicting feelings that you had about them. Miss the finale? Not a chance.
There is no comparing the shows.
And let's take a moment to remember poor Uncle Andy from Weeds. I cannot think of a more thoroughly despicable character. Shortly after the show ended, a network picked his unctious ass up and wrote an awful show around him called "Animal Hospital" or some crap. The Network literally cut away halfway through the closing ceremonies of the Beijing Olympic games in order to force that down America's throats. I think they only showed one more episode before pulling the plug on it. So much for capitalizing on Weeds' success.