We spoke with Charlie just minutes after Roethlisberger retired on Thursday ... and the former NFL quarterback explained he thinks Ben is hands down a better QB than Manning and Rivers.

"It's no knock against Eli or Philip, but I'm taking Ben Roethlisberger 1A," Batch said. "Eli 1B, and then Philip Rivers is behind them, only because of the Super Bowl victories."

Of course, Batch is biased -- he played with Ben for years in Pittsburgh -- but he said the guy was just that good.

In fact, Charlie tells us he instantly connected with Ben after he was taken in the first round of the '04 draft because they both played in the same college conference before they got their NFL starts.

“When I first met him back in 2004, there was instant respect because he went to Miami of Ohio and I went to Eastern Michigan," Batch said.

"So when you’re from the mid-American conference, we know how hard one, it is just to get to the NFL, and how hard two, it is to get there from the mid-American conference."

As for the Ben/Manning/Rivers debate ... Batch says even though he's got Ben on top of the heap, "all three of them will end up in Canton one day."

We also spoke with Batch about where the Steelers go from here now that Ben is retired, and he told us he believes they won't be able to pursue guys like Aaron Rodgers and Russell Wilson because they straight-up need all the draft capital it would take to acquire them.