It's definitively not an easy question. I'm in the same boat right now. I used to be a big fan of the GPL but in some ways I also like the BSD style licenses due to the amount of code it can be mesh with. I am not a lawyer so this not legal advice ;p

The questions come down to what kind of rights do you want to retain on the code when it's redistributed. GPL will force your users who redistribute the code in binary format to also provide the source and all the changes they made in to the code. It does not mean that they have to give back those changes if all they are doing is using it. Also all derivative works, like application that link to a GPL licensed library to open up that code too. (To avoid that you can licenses libraries under the LGPL)

BSD style licenses usually only force the users to keep the copyright statement you put in the header of the code on all future redistribution but makes not requirement on them to provide the code or anything, just that they keep the copyright statement. 

Most licenses are almost all just tweaks on these basic ones. 

I don't really know which one is best. There issues when trying to mesh GPL and BSD code together for example.

http://opensource.org/ has some good info on the different licenses.

Hope that helps.