Before I start, I just want to say that, no matter what people tell you, all of the people you have mentioned know a lot about boxing.
THE BREAKDOWN:
TEAM ESPN:
Brian Kenny
He hosts Fiday Night Fights and had hosted many shows such as Ringside and ESPN Big Fights which all have had many fighters on them and all about those fighters. Therefore he would have accumulated much knowledge about those boxers and boxers in general. His career on Sports Center would have added to his knowledge as well. His whole working life has basically surrounded sports, particularly boxing. He was awarded broadcaster of the year at one point.
Teddy Atlas
He is one the best boxing commentators as well as one of the best trainers in the sport of boxing. What he did to Mike Tyson in the amateur ranks is almost unmatched. He even was trained by Cus D'Amato when he was an amateur boxer himself. Atlas had also trained many great fighters, among them being the likes of Michael Moorer, Mike Tyson, Wilfred Benitez, Shannon Briggs & Barry McGuigan. He is the commentator for Friday Night Fights and judging by his fight analysis's and what he talks about, his knowledge of the sweet science is great.
Dan Rafael
I've seen him in a few interviews, particularly with Brian Kenny and what he says seems like he knows a fair amount about the sport. His prediction aren't always 100% but whose are? Not much else to say about him :)
TEAM HBO:
Larry Merchant
He used to be a sportswriter and is presently one of the best commentators in boxing. Dan Rafael even said he is the best boxing analyst ever. The boxers he commentates on aren't his biggest fans, with many of them having heated arguments with each other. Like the one time after a Floyd Mayweather fight, Merchant asked why Floyd is so boring. Similar occurrences happened with Tyson, Jones Jr and De La Hoya. His psot-fight interviews are very upfront. He doesn't really care what the boxers think about his question, he is just the only one brave enough to ask the boxers what the public actually want to know. This may be the reason for all the clashes he had with many boxers. He has a very vast knowledge of boxing.
Emanuel Steward
Steward was a boxer himself but only fought in the amateurs. He compiled a very good record, which can rival Mayweather's amateur record (Steward's = 95 wins-3 losses). He is currently a trainer and has been for years, with his most successful fighter being the great Thomas Hearns. When interviewed, he also answers thoroughly and truthfully, and always with a lot of knowledge.
Jim Lapley
He has been part of some of boxing's most famous moments. When you rematch the fights he commentated on you always recognized his voice and notable shouting. Remember the Tyson-Douglas upset, I can still remember him shouting when Douglas performed that combi and Tyson went down. "BUSTER DOUGLAS IS THE NEW HEAVYWEIGHT CHAMPION OF THE WORLD!!'
As for which I prefer. I would say I would rather hear from both, particularly Merchant and Atlas.
Good Question!