Put me firmly in the "Don is a better parent than Betty" camp. They are both horrible parents, of course, but Don shows a genuine love for his children that Betty simply does not seem to possess (at least after they grow old enough to speak). And the kids recognize that. One of the biggest examples of this is the episode in which Sally is afraid of baby Gene and Betty just gets angry at her while Don comforts her and sits with her holding the baby. And as someone else mentioned, Don recognizes that he is a shitty parent and knows he should do better. Betty honestly believes she is a great parent and is utterly confused and angered that Sally is acting out.
To join the broader debate about Don's character: He's certainly a bad person, but he is an incredibly sympathetic one as well. For one, his horrible childhood makes you feel for him, and his "self made man" characteristic makes you root for him. I mean, can anyone honestly say they didn't want to do a fist pump when he told Campbell in season one "You've never worked for anything in your life!" as Campbell was attempting to black mail him?
And despite his countless transgressions, the show has also been filled with small scenes in which Don has shown hints of a genuinely good human being--the moment with Sally mentioned above, the time when he chewed out the guys at the office for making fun of Freddy Rumsen's piss incident, when he defended Peggy against Duck in the latest episode, when he was clearly unamused by Roger's black face performance while others around him laughed, his mea culpa to Peggy "I will spend the rest of my life trying to hire you" (though not without self interest there too), etc etc etc. Hell, the very first scene of the show is him treating a black man as an equal, which we of course find nothing heroic about until this draws the ire of the man's employer and we are reminded that this is the 1960s, and that what Don is doing may actually be pretty admirable for the time.
To say that Don's just a dick and we're supposed to hate him is a gross oversimplification, and one that really doesn't do justice to his character at all. That's my two cents.