Graphs speak louder than words:
(From the Financial Times – behind subscription wall)
Thatcher and Blair are pretty good proxies for Republicans and Democrats, as they examplify respectively the hard "laisser-faire" deregulated economy of Reagan and Bush Jr and the centrist left policies of focusing more on inequality while fully accepting market mechanisms.
A third graph also shows how moderate Republicans do:

The conclusion: the left is much better for the economy overall. It provides increasing incomes to all, including the rich, but with a slight emphasis on the poor.
By contrast, Thatcherism is clearly class warfare: the richer get a lot richer, and the poor stay poor.
Moderate Republicans are actually the worst: they are not unfair, but they are pretty bad for eveybody.
Similar numbers for US presidents can be found in this article from Forbes. (with all the detailed statistics here):
It should be very easy to prepare similar graphs for the US economy (they probably already exist) and distribute them as widely as possible, as they show exactly what the differences between the two parties are, in an easily understandable way.
Borrow and Squander Republicans:
The rich get richer while you take on more debt.
They try to distract you from that fact by focusing on Schiavo.
Responsible, Fair Democrats:
Everybody gets richer and the economy grows for all.
One more thing – Extreme Republican policies have consequences that remain with you for a LONG time:

The inequality created by Republicans does not go away.
As a post scriptum, here are a few choice words from Martin Wolf, the senior economics editorialist of the Financial Times, about the unbalances with China, but which relates closely to this issue of economic competence:
If you owe your bank a hundred pounds, you have a problem. But if you owe a million, it has." John Maynard Keynes!>
If Keynes was right, the world’s creditor countries have a huge problem and the US none at all. Yet the assumption that the creditors should be more terrified than the debtor is wrong if the latter needs to continue borrowing. If creditors face an endless stream of additional borrowing and a good chance of default at the end of it, they should refuse to throw good money after bad. They will then impose huge costs on the debtor.
This balance of financial terror, as it has been called, characterises the current huge flows of finance to the US. Carefully thought through economic policy is needed if the world is to extricate itself from this predicament. Alas, we can rely on the administration of George W. Bush not to provide it.
(…)
100 per cent of the fiscal deficit has been financed from abroad and about 80 per cent of the current account deficit has been financed by foreign central banks.* Biting the hand that feeds one is folly.
According to the International Monetary Fund, the US general government fiscal deficit this year will be 4.4 per cent of gross domestic product, while the current account deficit is forecast to be 5.8 per cent of GDP. At present, therefore, the American people are able to consume and invest as if the fiscal deficits did not exist. The treasury secretary of what is arguably the most fiscally irresponsible US administration since the second world war should fall down on his knees in thanks rather than indulge in complaints.
Republicans are incompetents. Bush is the MOST incompetent of all Republicans. He is a threat to the well-being of a majority of Americans, and he actually is a national security risk.