Both Ezra Klein and Matt Yglesias have concluded that since Republicans are likely to fight any nominee,* Barack Obama might as well select a strong liberal who would rally Democrats going into the midterm elections.
What's odd about their comments is that they don't seem to take into account that a nominee perceived to be very liberal would be less likely to be confirmed than a nominee perceived to be a more moderate or "mainstream" liberal. They are right that, as Yglesias puts it, for conservatives "evaluating the nominee on the merits doesn’t seem to be an option." But that's not true about Snowe or Collins, and isn't even true about the handful of other Republicans who voted for Sotomayor. They will vote for someone who is perceived as similar to her, but might not for someone who is perceived as a liberal version of Robert Bork.
Given that, the idea that Obama will get a fight no matter what is incomplete. He'll certainly get a fight no matter what -- but a nominee perceived to be similar to Breyer, Ginsburg, or Sotomayor will yield a fight that Obama wins overwhelmingly, whereas a liberal hero could very well lose. And even if such a nominee manages to squeak through with 60 or 61 votes, marginal Dems will have to cast a tough vote, while the more moderate nominee forces marginal Republicans to cast the potentially damaging votes.
Yes, a fight is coming, but Obama has a lot to do with setting the terms.
By the way, a careful reader will have noticed a whole lot of "perceived to be"s in this post. That's deliberate. There are just huge error bars involved in predicting exactly how liberal or conservative someone will be on the Supreme Court. Even once they're on the Court, Justices move around quite a bit (see this graph from John Sides, using Martin-Quinn quantitative measurements of Supreme Court ideology).
Given all that, it seems to me that the added cost in the risk of failure isn't worth any potential benefit of goosing the Democratic base, and therefore Obama should nominate someone who Snowe and Collins will support. And it's not unlikely at all that his "mainstream" pick will wind up as liberal or more liberal than a liberal hero choice.
*Klein hits it: "President Obama could nominate the guy on the Quaker Oats box and Glenn Beck would find a way to connect him to Trotsky on his blackboard ("you know who else liked oatmeal!?")."
(UPDATE: Links fixed)