I've heard that it was a very controversial and contentious issue at that time, but have never really understood why it mattered all that much which was chosen. As I understand it different sections of the population favored one or the other. What were the rationale behind these positions?
It's not so much gold vs silver as it was the gold standard vs bi-metalism, or a system where both gold and silver are considered basis for legal tender. The reason why this was important was because gold plus silver obviously gives a higher amount of monetary units in the economy than if only gold was used, thus causing inflation and therefore decreasing the real value of of debt. Debtors in the country who were often farmers and the poor.
Staying on the gold standard on the other hand would have benefited creditors because the real value of the debt would be worth more without inflation. The political implications of this culminated in the nomination of William Bryan Jennings to the Democratic nomination in 1896 who declared that the gold standard was a tool of the wealthy capital and that "You shall not press down upon the brow of labor this crown of thorns, you shall not crucify mankind upon a cross of gold.".
The crisis was ultimately resolved by the increase in the global gold supply in the early 20th century and ultimately the partial abandonment of the gold standard under FDR and full abandonment under Nixon.