Here's how I see it:
Shawn Michaels forced into a match vs. Undertaker at WrestleMania... JBL doesn't want Shawn to be the one known for ending Undertaker's streak, interferes, and causes Shawn to lose the match. This leads to Undertaker going nuts on JBL because he prefers his WM matches to be left the fuck alone, or Shawn goes off on JBL, quits, and decides to go through everything the hard way.
This leads to Shawn and JBL going back and forth over the next year, both men digging in at shots at the World Heavyweight Championship with Orton... costing each other the belt along the way, and Orton always sliding out successfully (because if he loses the belt, he's qualified for termination). His belt will be his insurance policy. Eventually this all culminates in a WrestleMania 26 Falls Count Anywhere or Ladder Match. The Ladder Match would be favored by this time, as Shawn's still in financial trouble, if he wins, he gains his desired funds, if JBL wins, Shawn's got to retire, or JBL gets a title shot.
But to be honest, with the way the WWE is about people knowing the Taker matchup months in advance, I'm still siding with yet another undertaker vs. Kane WrestleMania match. Kane's coming to the point of retirement, as he's mulled over it in recent years. Undertaker wants Kane to be the guy to end his streak, he's told Vince he wont have it any other way. Kane doesn't seem too keen on doing that, but it would be the perfect leave for the Big Red Machine, and even Undertaker if he's still mulling over retirement. Send both monsters to Hell, and have that be it for the both of 'em, ending the era of the Brothers of Destruction.
Otherwise, the Umaga/Undertaker feud that was hinted at in recent weeks, seems to play out most favorably, and the HIAC match would be the most deserving.
Or Undertaker could opt to elongate this feud with Shelton Benjamin (nobody can deny they've had some incredible matches of late). Shelton wants to prove he's worth the shot at the WWE title... lasting with the Undertaker at WrestleMania would sell him over. And you wont find anyone more athletic or fundamentally sound as a mat technician than Shelton Benjamin... it could do his career wonders.