The Liberal Democrats’ two choices:
Door #1 (aka Nick-and-Dave, kissing-in-a-tree): at least two years in government, at worst a referendum on the alternative vote, most of your fiscal agenda (where you and the Tories agree) enacted into law, and probably some of the blame for the next year or so, followed by some of the credit for the recovery after that.
Door #2 (aka life with Ed Balls): a government that surely won’t last out the year, a referendum on STV (that probably won’t actually go into effect even if it passes until after the next election, since the government won’t last out the year—heck, the government may not even last long enough to pass an STV bill), some of the blame for the next year or so (but none of the credit for the recovery, because your government won’t last that long), and you get to have a big ugly fight on all the fiscal policy stuff with Labour, who campaigned on essentially the opposite platform from the LDP.
If only there weren’t that sticky issue called “ideology” in the way this one would be a no-brainer. But if the LibDems are serious about PR, they’re going to have to recognize that as kingmaker under a more proportional system they can’t be seen as simply the more respectable version of one of the two major parties—and that eventually they’ll have to work with both of them. Better for the rank-and-file who wistfully recall singing the Internationale in their youth before they sobered up to learn this lesson now than later, methinks.