I worked at an ad company that was very keen on social sharing. Having played with both the bookmarklet-style links you've cited as well as the official share buttons, I've found the official buttons are better supported. I feel like one day, Facebook is just going to deprecate sharer.php and make everyone use the Like button. Tracking aside, the Like button has a much better UX, whereas sharer.php has been barely maintained in spite of all the changes to Facebook proper in the last few years. I don't think you can even suggest a link title anymore.
Anecdotally, users seem to trust native button more. If it looks like you made your own PNG and linked it to Facebook, they can't trust that you aren't going to try to do something shady to their Facebook account (or open a popup). If you use Facebook's button, it's a familiar experience without providing the publisher's site the opportunity to play man-in-the-middle.
User perception matters. Facebook's button seems to be perceived as more user-friendly than the unknown button on someone else's site, even if the unfamiliar button was designed to be less hostile than Like.