They're both biased.
ESPN, RING, Showtime, and HBO all work in cahoots with each other. How do you think Brain Kenny goes from ESPN to Showtime or how Max Kellermen goes from ESPN to HBO or how ESPN always has the rights to show highlights from HBO and Showtime cards on Friday Night Fights. They're all together, "THE POWERS THAT BE".
What has to happen is fans have to develop their own opinions and stop letting the networks dictate who's a good fighter and who isn't. We as fans have to become informed, read the books, watch the old fights, and create our own rankings and understandings.
For a long time I used to buy into the whole Ring Ratings and ESPN Blah Blah Blah, but then I realized a lot of it is agenda based. Like how Roberto Guerrero magically pops on the Ring P4P rankings when he's fighting Mayweather who Golden Boy works with...but then again..that's just me...but its an example of how certain things in Boxing are scripted.
All these rankings are tainted with bias and politics. But I'd trust ESPN more because Ring is owned by a promoter and former fighter so there could be more bias in there.
I lost my respect for the ring mag ever since De La Hoya took over.
For me I trust Espn rankings more they have fighthers who are suppose to be in the top 10 list.Ring Megazine have alot of guys who shouldnt be on the pound for pound list.