I don't know what the best would be but I don't think I would use armor all. Haven't heard a lot of good things about it.
One dealer said they carry a cleaner for the panels. Not sure if worth it.
I was thinking about using just a silicone spray. but I would tyr a spot first.
I would use just about anything EXCEPT ARMOR ALL. Household cleaners like 409, Windex, etc would work just fine. However, my personal favorite is EAGLE ONE WET WIPE AND SHINE. Makes the plastic a little shiny and if it gets on the paint, it clean and shine it up also (I also use on the paint - great for quick shine-ups).
It can be found at just about any Auto Zone, Pep Boys, Walmart, etc. If you can't find this particular product, there are many others just like it, like Meguairs quick shine, etc. Just look around at the auto wax area of the store and you'll find them.