Ooh!!! This is a tough one.... Here goes nothing!
Obie I think is the easiest. He would definitely want to zip into the future and see his future family. More than anything he wants to be a husband and father, so I can see him wanting to take a sneak peek!
Xander would likely go back in time to the one night he spent with Walker. It's bittersweet, but he hasn't felt truly alive since that night. I think he would want to relive the one moment when he knew beyond a shadow of a doubt, she was his... as fleeting as it was.
Walker probably wouldn't go anywhere. There's nothing in her past she truly cares to revisit (good or bad) and she wouldn't want the anxiety of waiting to fulfill her now-known future. She would rather just live her life, having each day be a surprise.