I’ve lived in San Diego and thought finding housing there was hard but it’s a cakewalk compared to the hell that is finding an apartment in Amsterdam. I’ve considered leaving the city at times because finding somewhere decent here that’s also affordable seems close to impossible.
Hardest: SF, though it sounds easy compared to many of the experiences in Europe in this comment thread. As long as you have tech money, you should be able to find some shithole to live in. Even recent immigrants were fine as long as they came for good jobs.
Easiest: Tokyo, even with the famous (exaggerated imo) discrimination against foreigners I was able to find more nice apartments walking distance of my office within my budget, who said on the phone they were okay with a foreigner, than I could realistically look at in person.