4. Hank
When revisiting the Breaking Bad episode in which Saul Goodman makes his first appearance (episode 8 of season 2, also titled Better Call Saul), it is apparent that Hank may have some history with Saul. Saul arrives to Badger's aid whilst he is being interrogated by Hank and Steve Gomez and lays a legal smack down on the DEA officers who both realise that they have been bested. The looks on their faces suggest that they have had to deal with the shady lawyer before. They don't even attempt to argue back, fully well knowing that Saul knows every trick and loophole in the big book of law. It would be terrific to get the chance to see Saul get on the wrong side of all of the New Mexico crime-fighting agencies. Dean Norris portrayed one of the most interesting and entertaining characters in Breaking Bad and I'm sure nobody would object to seeing him now and then in Better Call Saul, even if it's only for a single episode in which Saul has to defend another drug dealer who is in trouble with the DEA, perhaps Skinny Pete or Combo.