Haven't seen The Sopranos, but The Wire didn't lose steam. It made steam. It gave you water, heated it up for you, and then gave you a fan to blow the steam in your face.
The Wire is the only show I would put in front of Breaking Bad in terms of quality.
^
Your first mistake.
Best show in television history and it's not even close.
All shows have dead cycles.
1) Sopranos - Season 6.
2) Andy Griffith - Anything in color
3) Frasier - Anything much after Niles/Daphne get married
4) Seinfeld - The finale
5) Dexter - Anything much after third season
6) Oz - The last season
Breaking Bad hasn't really had that dud year(s). But it's still not on the same level as Sopranos, even if you pretend Season 6 did exist.
No show ever has packed more foreshadowing, more detail, more info, more event into an hour than Sopranos. It all ties together from the first day. When you've watched it all the way through and then go back and pick up a random episode, it's like an entire season of drama bound into that one piece.
Best show ever.