I think about this a bit differently. What I want to do is to make it as likely as possible for my still wearable clothes to have a second life, preferably without having to travel across the world (usually again) first. So anything that I don't send to Twice to resell goes to my local Savers, which is a thrift department store that keeps most of the items they receive to sell, rather than baling them up and mailing them to Africa, like a lot of the drop off boxes in parking lots, etc., do. Savers is a for profit, but it's efficiently run and partners with local nonprofits to share a percentage of its profits. I know from seeing my old items in the store that things really do stay in house rather than being cherry picked by volunteers or resold online, both of which I've heard about happening at nonprofit thrift stores.
If there is a Dress for Success or a shelter in your area that wants your stuff and will use it, I think that's a great option.
