It's always a hard choice to make. It's easy to dismiss that all these homeless please are junkies/lazy/made bad choices and blame them for it. To me, that demonstrates a real lack of humanity towards our fellow man. We've become a very callous people. Unless something happens to a child we tend not to care and sometimes not even then.
My town (San Luis Obispo, CA) is a college town and we've been getting a bit of a homeless problem. You have your fair share of "typical bums" but since the recession started you've had a steady stream of younger folks.
A lot of the college age students shocked me because most people that young have some place else they can go. I've seen signs ranging from "Need help for tuition" or "Anything will help. I'll work if you want me to." THEN we have the homeless couple who have been begging outside of Food For Less for five years. Every time I go to the market he has a different sign "Have cancer, please help", "Vietnam Vet, needs help" and just about everything else you can think of that will pull on your heartstrings.
I'm more apt to give a dollar to college kids than I am to the established homeless couple. I'm not sure why, maybe because it's unusual. I barely have money myself and when I do don't carry cash but on the occasion when I did have a few bills I gave one to a kid I made him tell me his story first and asked pointed questions and in my opinion was telling the truth. It's that or he was a good actor.