Difficult and Highly Competitive. The US has the most complex and lengthy pathway to permanent residency (Green Card) for international students. It is almost entirely dependent on employer sponsorship and involves a significant element of luck due to the H-1B visa lottery system.
The entire process hinges on two main hurdles: winning the H-1B lottery and finding an employer willing to sponsor the very long and costly Green Card process. The 3-year duration for STEM OPT graduates provides more attempts at the lottery, making it a significant advantage.