First, the consequences of a default and a dollar crash would, at least in the short-term, likely not be the same. Also it depends on how you define 'crash'. A semi-controlled devaluation of 50% over 2 to 5 years? Worse?
In the case of a default (assuming an actual default and not a blip/technical default), all dollar-based credit, and by extension all dollar-based trade, would virtually grind to a halt. Take a look at the Baltic Index to see what happened in '08 to get an idea.
Although there might be a few short-term spikes in commodities like gold, with global credit disappearing, commodities would crash. $1150 gold, $45 oil.
So you have two major global problems: no trade; and, dropping commodity prices. Add to that the fact that U.S. long-term interest rates would be pushing towards 6% (or higher if no resolution was in sight) and the USD fluctuating madly - there would be spikes upwards as the default would result in a shortage and institutions would have to cover their exposure - and significant drops.
So those least exposed to a default would have little in the way of dollar-based exports, a strong balance of payments, little international debt owed, and internal trade/manufacturing/production. Or those countries in which the situation can't get any/much worse. Longer term, countries with an internal infrastructure and the ability to feed themselves will likely be in fairly strong positions.
With all of this in mind, I'd pick Uruguay (also the only country in the Americas not to suffer a recession in the '07 - '09 period).
Or perhaps Alaska (though it could be sold back to Russia to pay off debts.)
Also keep in mind that if a default transpires, that China and other US creditors will own the US. The US stock market will fall be 15% to 30% (2011 study by Credit Suisse). At the same time the US gov't holdings of the Chinese (and other) government will have dropped in value. The creditors won't be able to sell the debt holdings all at once so they'll be better off using those funds to buy up devalued US dollar (or pegged currency) based assets while they confiscate (or at least threaten to) US corporate assets in China as payment.
As for the devaluation - just look at what's happened since the 1913 meeting on Jekyll Island and draw your own conclusions.
tl;dr Uruguay or Alaska