A reasonable question, but there is no single all-around lens, period.
Think of at least one wide, one "normal" (50mm equivalent), one short- to medium tele.
And that's still as impossible a reduction as looking for just one. If I absolutely had to choose just one, it wouldn't be a zoom... it would be a fast prime that worked out being roughly a 50mm or slightly longer equivalent on the specific camera I was getting it for.
Others would say the same thing, only 35mm or slightly shorter.
Others would damn the torpedoes, and get a zoom, even if it wasn't very fast.
If it's a matter of funds, start with something good in the middle, and then add the short and long. Save money by shopping on eBay, but get quality. And don't think that you can ever get by with just one.
One last thought, and just my opinion: it's infinitely better to get up and walk all over the place, than sit still and zoom. Don't. Just don't.
P.S. - to answer your question, instead of dancing around it? One of the f/.95 primes, depending on your camera. Probably one of the two Voightlanders... 17.5mm for the Pocket, 25mm for the BMCC. Just my personal choice. I am planning on getting the 17.5mm Voigtlander as my dream lens for the Pocket. Difficult to match for my BMCC EF... perhaps the Zeiss 25mm f/2.0.
I'll say it again - Prime and move around, vs. static and zoom. Always.