Why do people say that Iraq was more stable under Saddam Hussein but don't say that Germany was more stable under Adolf Hitler? (don't forget that Germany was going through a depression before Hitler came to power)

The two halves of your question are unconnected.

Both men were evil but the comment that Iraq was more stable under Saddam than during the chaos that followed is obvious. The warring Islamic factions are struggling for power and rebuff any foreign attempt to stabilise the country.

Following Hitler's demise the was a period of deprivation but the German people worked together to establish a nation that was to become one of the world's economic success stories.

There is no comparison between post-war Iraq and post-war Germany.

The following link is the only reason for Saddam to have continued ruling and it's kind of weak.

Whereas Hitler cleaned up unemployment and helped Germany progress for a few years, his Third Reich was the essence of evil led by a madman. The people were happy till they saw through the facade.

The news there for Saddam says it all.

Related: How Saddam Hussein Made the Middle East Stable