Dark Knight Returns/Dark Knight Strikes Again: Would have been cool, but it no longer fits within continuity. Too much tweaking would be required to make it work. Modern Selina Kyle is not going to become a fat madame, Jason is not the last Robin, Nightwing is not going to turn out all ****ed up like that, etc. The world is not going to surrender to that kind of darkness.
Batman Beyond: If there is a new Batman, it will be Dick or Tim. At one time, Cass could even have filled Bruce's shoes. But not some no-name Terry McGuinness mother****er. Nice show, and it worked for the DCAU, but not in our house. Also, I'm uncomfortable with a Bat-future THAT ****ed up. All that wierd Dick-Babs-Bruce triangle crap, and all the other stuff...no. Batman was supposed to end up with Selina in that universe, and I was always pissed that it didn't happen. Of course, I think Batman should end up with Selina in the DCU too...
League of Batmen: Also could have been really cool, but the kid's not named Tallant. And he's a little punkass. No way does he grow up to defy Ra's like that.
Kingdom Come: This one could have been my top choice. For awhile it looked like Superman-Batman was making a concerted effort to make KC canon. But Wesley Dodds' death at the beginning is pretty important to the story--and Wesley already died.
Earth-2 Batman: This is yet another gem. He retires, becomes commissioner, and dies in one last heroic fight to save his fellow heroes. However, given the current Batman's outlook, it's not likely to happen. When he has to retire, he'll continue running things like in KC.
Titans Tomorrow: This one, I think, has already been cancelled. The Big Three didn't die in the Crisis. I'm pretty sure this one's out of the picture, and good riddance to it. It was an interesting possibility, but it's gone now.
In the end, it's not a matter of what future I'd prefer, it's a matter of which one is most likely to happen, if DC ever decides to make one official: it has to be the One Million future, also compatible with the Legion of Super-Heroes future. These are futures with well-established ties to current continuity. They're going to happen. They're not the futures I'd have chosen, and if people could let the Legion drift off into an alternate universe or timestream and stop this incessant time**** that the DCU always has going on, maybe this wouldn't have to be the future. One Million could be retconned out by any number of perfectly explainable phenomena involving Hourman.
If they could come up with another character death to be similar to Wesley Dodds' in Kingdom Come, I'd choose KC as my favorite alternate future. That's just me.