As an immigrant (first in the UK after than in the US, followed by return to the UK), I can say the annoying things about different systems are unpredictability and long delays. I agree that it is up to every country to set up the rules who gets to stay and under what conditions, but they need to be clear and predictable. I have found the UK system reasonable (although expensive) with a standard path of 5 years of working visa, followed by the indefinite leave to remain (green card) and then citizenship application (after another year). My impression of the US process was much worse with year long queues depending on nationality, quotas that are taken in first few days etc, and rules being changed on the hoof (in the last administration). I think that creates a really bad climate for people. And I do think the countries are responsible for making sure that migrants are treated fairly with clear well understood rules that are not changed unpredictably. For me this was one of the reason to go back to the UK as I didn't want to jump again through all the immigration hoops in the USA.