Suppose we can give each member of congress a score, from 0 to 100 (0 meaning 'extremely left-wing', 100 meaning 'extremely right-wing'), so that for every piece of legislation that comes before them, there exists a threshold wherein the probability that everyone with a score under the threshold votes one way, while everyone with a score over the threshold votes the other way, is very high indeed. Suppose further that there is perfect polarization between the two major parties (every Republican's score is greater than every Democrat's score, every Republican's score is closer to the typical Republican's score than to any Democrat's score, and every Democrat's score is closer to the typical Democrat's score than to any Republican's score).
In the house of representatives, the effective decision rule is majoritarian--that is, a piece of legislation is approved if and only if a majority of representatives vote for it. The fate of a bill, then, stands or falls with the vote of the median representative: if the median representative votes 'yea', then either everyone to his left or everyone to his right, with very high probability, votes 'yea', constituting a majority in favor of the bill. Similarly, if the median representative votes 'nay', then there is, with very a high probability, no majority in favor of the bill. In effect, one representative makes the decisions for the house. The bigger the majority party's majority, the more the favorable approved legislation is to the party's typical member.
In the senate, the effective decision rule (these days) is supermajoritarian--that is, a piece of legislation is approved if and only if 3/5ths of senators vote for it. The fate of a bill, then, stands or falls with the vote of both the 60th most left-wing senator and the 60th most right-wing senator. Unless the majority party enjoys a supermajority, approved legislation is most favorable to the centrists in both parties.
If one party is more polarized than the other, then approved legislation will be biased in favor of the more polarized party, other things being equal.
During 2009-2010, the Democrats enjoyed a large majority in the house, and a bare supermajority in the senate. They also held the white house. Due to polarization, one-party control leads to greater legislative output. The house's output, in light of its large but not extreme majority, was left/center-left. The senate's output, in light of its bare supermajority, was center/center-left. And the president, having to appeal not only to his party's base (extreme left/left), but also to Democratic-leaning independents (center/center-left), was left/center-left. Overall, then, the government was center-left, or slightly left of that, with lots of output.
During 2011-present, the Republicans enjoy a large majority in the house, while the Democrats cling to a bare majority in the senate. Democrats continue to hold the white house. Due to polarization, two-party control leads to lesser legislative output. The house's output, in light of its large majority, has been right/center-right. The senate's output, in light of the Democrat's bare majority, was centrist. Again, the president was left/center-left. Overall, then, the government was roughly centrist, with little output.
Intrade predicts that Republicans will control both houses of congress in 2013, though probably without a supermajority in the senate. Hence, if Obama is re-elected, we will probably see a slight shift to the right, with little output. If, on the other hand, the Republicans take the white house, we should expect a much bigger rightward shift, and much more output.
From a historical perspective, the DW-NOMINATE system, devised by political scientists, shows that this basic model is plausible, and that the Republicans have become more polarized than the Democrats over the last few decades. This biases these results even more in favor of Republicans. The choice, then, is between a center/center-right government, and a right/center-right government. From a global perspective, the US is significantly to the right of most developed countries. Therefore, the choice is, in some ways, between a center-right government and a right-wing government.
Note that none of these terms are defined with respect to issues--purely with respect to patterns in voting behavior. So, if you're someone who thinks anarcho-capitalism is a moderate position, then redefine the terms I used above appropriately. Another way of saying it, then, is that we're likely to be looking at a choice between a moderate Republican government (in the old sense), and a fairly hardcore Republican government (in the current sense). Take your pick.