Spring (march) is the best time to photograph Iguazu falls with full water and good weather. However stormy weather at other times of the year can produce dramatic lighting. You can see both the Argentine and Brazilian sides of the falls from Puerto Iguazu in Argentina (recommended) or Foz do Iguazu in Brazil. Bring a raincover for your camera- the mist can get pretty heavy.
"You hear it before you see it. You feel it before you hear it, through the soles of your feet, in the chambers of your soulâ€”a low rumble, the very ground thrumming beneath you. Step to the edge. A gust of wet wind and the earth falls away in this great leap into the abyss." -Jeff Rennicke from National Geographic. Runoff from the heaviest rains in 25 years funnel over the cliffs of Iguazu Falls, one of the greatest natural wonders on the planet.