Which is the more commonly used word?

My purely anecdotal experience is that a native speaker would say "more polite."

I agree with Setanta, giving you a view from both sides of the pond.

Thanks, McTag and Setanta.

It's interesting how dictionaries can 'mislead'. I can find 'politer' in dictionaries, but no luck with 'more polite'. Despite that, 'more polite' is more natural among native speaker.

that's because "more polite" isn't a word, but a combination of two words in conjunction that clearly follows common usage(there's no easy way a dictionary could list all the possible uses of "more ----", there would be tens of thousands of them). But "politer" is a word, tho not a particularly commonly-used one.

Dictionaries, even the good ones, make mistakes, Ms Tan. OED took until about 1998 to declare the split infinitive okay. Many dictionaries still list modal verbs as present or past tense forms of other modals when they are never used in such a fashion in the English language.

Both AHD and MW list 'politer' and 'politest' in their entries for the adjective 'polite'.

It would be interesting to see corpus studies on which is more common.

Thanks to all of you.