This is a tricky question.
On average "GoT" has more viewers, but the final 4 episodes of "BB" were higher than any episode of "GoT", and the finale had 10.2 million viewers, twice as much as the most watched episode of "GoT".
Also "BB" is the most watched show on Netflix in the U.S.:
http://www.cnet.com/news/breaking-bad-is-top-netflix-us-show-doctor-who-in-top-10/
Obviously there's no equivalent for "GoT" since it's on HBO.
To be fair I'd say over all "GoT" might be more popular....but I doubt it will ever reach what season 5 of "BB" did, either in viewership or pop culture relevance.
As far as which is better....the people that write "GoT" think "BB" is the GOAT, and the actors are all huge fans. GRR Martin himself wrote a blog about "BB" the day "Ozymandias" aired.
And that speaks for itself really.
Now here's a picture of Jesse Pinkman and Melisandre:
Fred.