Most Helpful Girl
I think polkadots are okay, if done right (since it is really easy to cross the line into "childish" territory with that sort of thing). For example, I have a 50's style summer dress that's white with dark red polkadots and whenever I wear it in the summer I always get a lot of compliments on it from both men and women. So personally, I think polkadots are fine if they're done in an age-appropriate manner.
But for the most part I have to agree with what others have said here and say stripes. They just seem to be more acceptable and speaking from a style perspective, they're a heck of a lot more versatile than something that's polkadotted.