You might think the answer is the Swiss Franc, or the Euro, or the Yen. Alas, you would be wrong on all three counts.
Over the last ten years, the average annual depreciation of each of these paper fiat monies, against gold, was the following:
The average annual depreciation figures over ten years for the dollar and the pound are as follows:
So if you were saving pounds in a bank account for the whole of the 21st century so far, your bank would have needed to give you 14.69% in net interest every year for ten years (using a geometric progression rather than an arithmetic average progression), merely to hold the value of your paper money steady against gold.
To make that simpler, £100 pounds ten years ago had the same buying power against gold as £380 pounds has now, which is almost four times more valuable. This is how government's rob people through central bank money supply inflation, without their tax proles ever really noticing. If you're doing the same kind of job you were ten years ago, are you being paid 4x as much? Think about what kind of job you had back then, if you've been promoted or moved into a different line of business. Is someone in a similar position earning 4x as much as you did back then?
And remember, back in the glorious age of deflation, from 1815 through to 1914, most wages stayed the same over the whole period (in gold) but prices would go down almost each and every year, except in years when the state managed to induce wars to increase their power over the people. Now, as well as being paid less each year in terms of gold, prices continually go up.
We really have been sold the most enormous pup, by the Keynesians.
For more information, try here:
=> THE DECADE'S BEST NATIONAL CURRENCY
So what's the answer to the question, then? Well, for that we first need to define what money is:
mon·eyAccording to the primary definition of money above, the best form of 21st century money, or that which holds its value the most over time, is gold. The second best form is silver.
n. pl. mon·eys or mon·ies
1. A medium that can be exchanged for goods and services and is used as a measure of their values on the market, including among its forms a commodity such as gold, an officially issued coin or note, or a deposit in a checking account or other readily liquefiable account.
The Austrians are coming, everyone. Can you hear them?
Oh, sorry. I'm actually wrong about that, aren't I. Because the credit-crunch recession is now over. Welcome to the recovery.