The Egyptian star is facing an uncertain future at Anfield with his contract at the club due to expire next summer.
While the 29-year-old's did ease the concern by revealing that he'll be sticking around at the club for next season at least, his long-term future at the club is still in doubt.
The same can't be said for Mane, however, with the Senegalese star being heavily linked with a move to Bayern Munich this summer.
It's plausible that Liverpool could be set to lose at least one of Jurgen Klopp's best players, but according to Cascarino, it's a no-brainer that Salah should be kept if he wants to stick around.
Asked who he prefer to keep, lifelong Liverpool fan and former Republic of Ireland striker Cascarino told the Weekend Sports Breakfast: "I would still go Salah, only slightly, but if Salah wanted to leave more than Mane I'd let Salah go.
"That's how I feel. I'd want the one who is most committed to stay, and hopefully both of them feel that way.
"He seems to have this real belief.
"I believe that Salah is a player who will always cause problems for teams because defenders hate playing against them. He wants to run behind them.
"Even when he's not playing well, he'll still do the things that make him such a great player.
"He sometimes mis-controls things, but he never stops trying to do it and that's what Klopp really loves about him.
"There isn't a switch-off with Mo Salah. He always wants the ball, always, and that's what stands out with Salah."
He added: "I don't think he's been the best player in the world in the second half of the season.
"He got 22 goals in 27 games before the Chelsea game at the turn of the year, so he was absolutely flying, and then after that he's got nine in 27."
Cascarino even shared some positive words about Salah's relationship with Trent Alexander-Arnold down the right flank, describing it as 'one of the best relationships' he's even seen.
He said: "Salah allows Trent [Alexander-Arnold] to get in positions of danger. Mo does that brilliantly for him, their relationship is incredible.
"It goes a little bit under the radar because we talk about their individual ability, but as a team, they work in tandem brilliantly.
"They're as good together as any full-back and winger that I've seen in the game."