I think Christian should definitely take Money in the Bank, it's his time after waiting so long.
An Edge/Christian feud any way you slice it will be amazing but for best results it's gotta be Heel Edge vs. Face Christian. Here's how I see things going.
Wrestlemania: Edge wins WHC, Christian wins MITB
They stay away from each other with just Christian mentioning Edge (And WWE Champion) by name the Raw after Mania. Christian enters a mini feud with anybody really just to build his credibility. Christian takes the Face MITB route and announces he's cashing in at the MITB PPV against his brother/friend/whatever they're calling them Edge.
The build up is top notch with Christian one upping Edge every week on Smackdown. They even tag together against ShowMiz or whatever team is holding the tag titles by then. Christian says on The Peep Show he's that much better than Edge, head to head, he always was. MITB comes around and they put on a classic, lightening fast counters telling the story that they know what the other is up to. Ref bump comes and Edge is out of moves to throw at Christian who is proving resilient. Edge grabs two chairs and sets up for the One Man Con Chair To but Christian sweeps his legs and sets up for the Killswitch. Edge shoves him away and drills a Spear which leads into a pin with the ref getting up. Christian kicks out and Edge is livid, he sets Christian up for the spear again but instead grabs the chair and wails on him. DQ, followed by a Con Chair To. They continue the feud this time personal and end it in a TLC at Summerslam.