It's a hard choice.
Dick- Already has established himself as Nightwing, getting away from Bruce... But now they're back to being a family again, though still doing their own things when they're not needed. I love Dick as Nightwing, I love his origin and everything, and to have him be Bruce's successor seems logical as he's the best match for it- but he worked so hard to form his own identity away from just being a sidekick.
Tim's been doing fine as Robin. As the leader of the Titans he has his own responsibilities and authority, and the identity is suiting him well. Shown as Batman in Titans Tomorrow and he would make a good Batman, it's just what would happen with the Titans, and with him taking up Batman's mantle what about Robin's mantle, and the age thing, etc.
Jason... Just... Nah. It was strange that they brought him back, it was strange they made him a "major" player in Countdown. But DC surely know that he's not well liked. And he's busy dealing with the crisis, universe jumping etc.... Not to mention he just became Red Robin this week, a new and significant identity (and another Kingdom Come entrance). They also had an alternate universe where he met himself from there having taken up the Batman title, which I just saw as an acknowledgement of him as Batman. Then again, so have the other three.
It'd just be too messy if Bruce were to die permanently. For one, it's pretty much impossible- not because he's so "lolbatman", but because of all the different ways he could come back; including alternate universe batmans, and lazarus pits (they JUST brought Ghul back). Also, he's such a major player in DC- He's JUST become the leader of the Outsiders, and that title is only a few issues in. It's just weird to put all that effort into starting a new title to have it stop, or have them leaderless, or go back to being the Outsiders... Or if a new Batman took over that would just create all kinds of issues.
My opinion? Kill him temporarilly or have him go missing- just to show what it'd be like, like with Superman's death(s). DON'T have anyone else become Batman- have the others take care of things while he's gone. I'd say Nightwing is pretty much equal to Batman- easilly a substitute for him temporarilly, just would lose to batman if they ever faced off in any form of competition. Tim is arguably an even better detective, but his youth, though advantageous in him lasting, also limits him, as well as his responsibilities (they all have responsibilities, so you have to have multiple people help out filling in for Batman so they don't neglect their own duties); Oracle taking care of the investigation/ information/ detective work, the current Batgirl helping out however she can (not so familiar with her), and, finally, a nice opportunity to have Batwoman and Renee (Question) back on the scene, as together they're a good Batman combo. So basically... Bruce disappears for a while, and a 'colony/ cloud' of the whole extended Bat family network filling in.