It ain't Christian McCaffrey, Breece Hall or Bijan Robinson ... no, the best tailback in the NFL is Alvin Kamara!!

... at least, that's according to the Saints star's teammate, Demario Davis, who tells TMZ Sports he's sure no one else in the league is as good a runner as Kamara.

Davis didn't mince words when we talked to him this week following AK's four-touchdown performance against the Dallas Cowboys ... saying point blank Kamara's the NFL's top dog.

"Going against Alvin all these years," the New Orleans linebacker explained, "I've repeatedly said that he's the best running back in football."

There were, of course, years where no one would have disputed that ... but entering his age 29 season -- there were plenty of non-Kamara believers this offseason.

But with the halfback already totaling 198 rushing yards, 92 receiving yards and five total touchdowns ... Davis is making it clear it's time for the haters to clam up.

"I think everybody should probably try to get him on their fantasy team," he added.

We also spoke to Davis about the Saints' 2-0 start ... and while many NFL fans didn't see it coming -- it sure seems like he's been a believer from the get-go.

Additionally, Davis told us in between helping New Orleans get off to an undefeated start -- he's been assisting in his community ... partnering with Ashley HomeStore to help families in need get some big home makeovers.