None of them. In the absence of Iginla, it's pretty clear Regehr is the leader of this team, but as has already been mentioned, if Iginla goes, Regehr is hot on his heels.
After that, the 'leadership' on this team really dives off; the most talented player on the team is probably J-Bo, but him as a captain makes zero sense to me. Giordano probably has the biggest heart on the team, but I don't see him as true 'captain' material. Beyond that, you've got a laundry list of guys who are 'A' material at best. Bourque would be the team's best forward, but it appears that he's not really a 'leader' so much as he's a guy who goes out and does his job.
After those guys, what have the Flames got?
Joker- Hell no.
Tangs- Not likely; hates the spotlight.
Morrison- No, esp. considering he's a 35 year old one-year player who'd be dealt at the deadline for picks if the Flames rebuild.
Conroy- No, he's retired after this year, if he doesn't get waived/traded earlier.
Glencross- Ferraro made a comment a few games ago about GlenX sometimes shutting down when things don't go his way; pass.
Moss- Makes J-Bo look like he's got all the fire of a southern black Baptist minister.
Sarich- Gonna be traded/not a captain anyway.
Staios- Hellllllll no.
Backlund- WAYYYY too young.
White- He's probably gone too with Regehr and Iggy.
So in conclusion... pretty much this team would need to roll with a series of A's until Brayden Schenn is ready to assume the matrix of leadership