Window films will not stick to plastic. The plastic out-gases, and the tint will end up bubbling. If you go with plexi, just get it smoked to begin with.
If you have clear glass, and decide to get it tinted, you'll have to use a 35%-20% smoked film. Make sure it is non-metallized, or it will have a semi-refective appearance.
Since this thread is alive again, I can dispel this statement as it applies to us... I think the gassing of plastic occurs in sunlight and heat. I've had the plexi bezel on my bartop tinted with 35% auto tint for almost one year now with no bubbles.