I think that it's most likely that we will see Shawn go out to Triple H. Remember Wrestlemania 20, when they were both going to finally settle their differences, it never happened because of Chris Benoit's Rumble win.
It seems logical, and in November, WWE has a DX RAW tour in the UK. As I found out at the RAW tapings last night. It's basically just RAW, but the DX part indicates that The Game and The Show Stopper will re-unite DX again. With Shawn Michaels career ending in sight, perhaps we will have a situation where Shawn announces he will be having his final match at Wrestlemania 26. Triple H some how helps HBK win the WWE Title again. Then Shawn is the Champ going into Wrestlemania 26. DX running wild. BAM! Trips turns on HBK. Either that or they mutually agree to wrestle each other at 'Mania, and they gradually become more and more competitive towards the event.
I don't particuarlly want to see Shawn go out as a heel but it's an option.
John Morrison would be a great pick against The Heartbreak Kid.
What about Matt Hardy? If he gets the limelight when/if Jeff departs. Or even Jeff against Shawn if he stays?
As for The Undertaker. I think John Cena would be alright. It would sure be a Main Event Match. But personally, I wouldn't want to see The Undertaker, the Phenom, go out to John Cena who is the kids favourite, lets face it, he is.
Again, perhaps one of the Hardy brothers? Not likely to be able to go legitamately over The Undertaker though.
Kane I don't think has enough time left in him to be put over for that kind of honor.
Chris Jericho? Now this is a match everyone's wanted to see. WWE could tout it throughout this year now with Jericho on Smackdown! It could be an epic match. Jericho argues; he ended the careers of three legends last year, he has beaten Shawn Michaels many times, all that remains is the Undertaker's streak.
Batista? Who?
I really have discovered that this guy is, without a doubt OVER RATED. As far as I'm concerned I don't even think that he needs an offical retirement match. He can just fade into the wallpaper for all I care. His retirement is no way near as big a deal as The Undertaker's and Shawn Michaels'.
As for which one would take the main event? It would have to be The Demon of Death Valley. The man's legacy is built on Wrestlemania, and being undefeated at the event. Shawn Michaels, ABSOLUTELY all due respect here; Is Mr. Wrestlemania, but not Mr. Undefeated at Wrestlemania. Wrestlemania is more 'Taker's event than Shawn's.