Depends on what they are on. If it is stripes on clothing, depends on which way they are going. vertical stripes ok, horizontal, not so much. Guess I better stick with polkadots. (Just answering polkadots was too short of an answer.)
I personally LOVE polka dots! Stripes can be tricky if they are on clothing, it is important that strips run vertical. Otherwise, stripes can be a fun look as well, depending on their width. Narrow stripes look more classic and sophisticated, while equal sized stripes are more youthful and playful. Polka dots can be sophisticated when it is a solid white dot against a strong solid background, and more playful when using multiple colors of dots or variegated colors in the background. However, given a black and white choice, I would always choose polka dots!
I love both. Polka dots have a feeling of youth, warm weather and freshness about them. Stipes can be very conservative, such as a pinstripe suit or skirt, but they can also be fun, flirty, and of, course, nauttical. Why either or? Why not yes, to both?
Hmm. Imagining either is kind of disturbing to me. Thinking, thinking... Nope. I'm not able to choose because I can't stand either. I'd have to know what they're on before I could choose the least obnoxious of them.