Which should I use in my application: Libglade or GtkBuilder?
You should use GtkBuilder if you can as GtkBuilder is expected to replace Libglade (Why?) and GtkBuilder is built right into GTK+ thus reducing your application’s dependencies. However, you (and your end users) will need at least GTK+ 2.12 and you will have to run the files you create with Glade through a conversion script until Glade 3 supports saving in the GtkBuilder format directly (When?). The vast majority of tutorials and large projects out there will still be using Libglade. Being that Libglade and GtkBuilder are so very similar in terms of the API, you shouldn’t have trouble using one or the other depending on what you’re working on. You don’t need to panic about using one or the other, just be aware that GtkBuilder is the future. If you have an application already using Libglade, you could switch now or wait until it’s better supported. However, I would recommend using GtkBuilder in new applications to avoid having to migrate the code later.