I'd take Leddy. Runner up is TJ Brodie. But i feel like there's a sort of weird perception overall that Leddy is somehow "older" and more likely to decline sooner. Probably because of when they hit the NHL, respectively. Even though that's clearly not the case.
For me, Leddy is a guy who can anchor a Top-4 D pairing, arguably even a pretty decent top-pairing...whereas Brodie tends to be a guy who needs a bit of babysitting if he's going to face tough matchups.
They're both very good defencemen though. And i wouldn't hesitate for an instant to take either of them over Gardiner.