How do you make the decision?

Sproles will be 30 next season.
PT will be 28 next season (actually next month).
Ivory will be 25 next season.
Ingram will be 23 next season (actually next month).

RB is the one position you have to constantly get younger at. I think we can all agree Sproles is safe due to his relationship with Brees and the limited wear on his body (never had over 100 rushes a season. Max touches were last season with 123).

PT has also had limited wear, but has also never played a full season until last season. He's also seeing his receptions go down this season despite having his highest ypc this year. Saw the field less and less in the past two games. Maybe the staff sees something else in the other backs they really like?

Ivory is a classic angry runner. He won't give you much in the pass game, but playactions to him will open things up. He'll pound defenses and soften them up. He might only do one thing, but he does it very well.

Ingram was a 1st round pick that didn't come cheap. I don't believe in harming the team to justify an expense, but Ingram has been looking good recently. He's finally showing what he can do and almost looks like a younger PT. The one complaint is in the passing game, but he is showing signs of improving there.

In terms of trade value, I think the order is:

Unless someone offers a ludicrous package, Sproles isn't going anywhere. PT has a team-friendly contract and is a proven, versatile RB. Ivory would probably net less of a return. Ingram's contract isn't bad, but the way the Saints have used him crippled his value.