I think you will find Tk-Perl will be the easiest to learn and you would find the most support for it. That is a big consideration. Gtk-Perl and Glade is a nice combination, but you will find it harder to find "howtos, books, and active forums" for it. Whereas with Tk, the comp.lang.perl.tk newsgroup has experts answering newbie questions everyday. Also the MainLoop event-driven loop style of programming is quite similar in concept, and concepts you learn in Tk can be transferred easily to Gtk.

P.S. I think the Gtk-perl interface is faster when running, if that is a consideration.