I'm sorry, but the entire premise that there is one "best" open source license is completely wrong. Where did this obsession arise to see one license crowned victor over all others, in all situations?
BSD (and MIT and variants) -- I've found they work best for providing backend and reference libraries, which by their nature are trying to provide a standard implementation of something, or at least a standard API. Open and closed sourced projects alike can use and modify it to suit their needs. This means such a library gets the widest adoption over the alternatives (all other factors being equal). This is especially great for server-side programs which want to promote multiple third-party clients - just release a BSD reference client.
LGPL -- A step down, for when you want the adoption level of a BSD license, but your project is complex and high maintenance enough that it needs to keep all the developers focused on a single api and codebase in order to thrive. Graphics libraries like GTK, audio processing libraries like LAME, are a great example of this.
GPL -- Finally, for the same reasons as LGPL, your want everyone contributing back to a single codebase, whether it's because you don't want to give the codebase away to closed source products that then profit from it, prevent brand confusion, or just maximize developer contributions. Mind you, closed source projects *will* choose an LGPL/BSD alternative over this or closed source, so it doesn't make much sense for libraries, etc. Primarily, this is useful for applications, which are vying for user (not developer) eyeballs.
So given they all have different uses that fit better for different project types and target markets, who in their right minds thinks only one of these licenses is correct?