The term "filler" is a highly subjective and abused term used for a "pointless" or "unimportant" episode. But that's like saying an ordinary day in your life means nothing. The plot is about traveling the world, sharing adventures with friends, and meeting new Pokemon and people. Therefore I don't consider any episode to be a filler.
I am the current leader of Save Our Voice Actors, a Pokemon fan group supporting the voice actors in the anime dubbed by 4Kids (seasons 1-8). Our goal is to provide The Pokemon Company international with encouraging feedback in support of returning the main cast members. If you're interested, please visit us at facebook.com/saveourvoiceactors