Why is the Euro a bad idea compared to other currencies?
One of the key requirements for a currency area to be successful is that there must be a sustainable political mandate to support fiscal transfers between regions, to provide the balancing mechanism that would otherwise have been performed by fluctuating currency rates between those regions.

Another is that labour can move freely between regions.

The Eurozone, it turns out, met neither of those requirements:

Language barriers have impaired freedom of movement.

And although Northern Europe was happy to reap the benefits of currency union during the good times, it has proven to be unwilling to make the fiscal transfers to the South during the bad times.

Exacerbating this, Greek admission to the Euro zone was created on the back of some fraudulent accounting courtesy of Goldman Sachs. Based on the real numbers, Greece would never have been admitted.