Goodwill isn't really a thrift store in the traditional sense. You're giving them stuff to sell at a decent price so they have money to hire people and donate money to other charitable causes. They're not a place to drop off stuff so it can get in the hands of poor people for free or cheap.
Of course, it's very admirable to donate things to the homeless shelters as well where they go directly to people who need them.
I usually go with goodwill as it's more convenient with more drop off locations etc.