Canada, Australia, and Germany have a pretty similar immigration process. Australia is the easiest out of the three, but they still only accept 1 immigrant per 10 we accept in the US, so I struggle to see how that's "easier." Germany is harder by every measure, and Canada is pretty similar in "difficulty" by most measures.

New Zealand and Spain you really couldn't be more wrong. Just for starters, both countries combined accept only ~50k immigrants per year (the US is 20x that).

If you calculate the "expected value" for a migrant from anywhere in the world, the best bet you can make will predict that they'll end up migrating into the US. From this metric, I'd judge that the US is the "easiest" destination.

Btw, I say this as an immigrant in the USA ;)