It depends.

If I want to read/watch something later, then it gets sent to Instapaper. If it's an article/site that I think I might want later, then it gets sent to Pinboard. If I want to quote something, then I post it to Tumblr. I've also got some IFTTT rules set up to save links to pinboard if I favourite on Twitter, post to Tumblr, like on Instapaper, etc. The goal for me is to make Pinboard the central repository of everything I want to remember; other services end up there if it's worth remembering.