san francisco hands down. the city spends an average of $10,000 per year on each homeless person. not to mention there's shitloads of tourist to give you spare change. I'm sure there's more in chicago and NYC but it rarely gets below 50 degrees in SF.
They do all the time, especially younger ones who were traveling. Try talking to a few homeless people on streetcars, you have all sorts. Young people who leech, old cast out drug addicts, mentally ill, ex-cons, boozers.
Orlando always seemed like a good place to be homeless. They have decent buses downtown, some shelters.. when my brother worked as a Mobil Friendly Serve attendant, one homeless guy who worked an I-4 offramp made upwards of $200 a day.