Instead of asking the dreaded "Which lens should I take?" question, I'm asking which lens did you take on vacation? How did you feel about your choice later? Great pictures and you had a blast? Great pictures and a sore back? Meh pictures and you didn't even notice your camera bag? And the worst possible result, you spent the whole trip wishing you had that lens you left at home.
I'll start: This spring, I went on a wildflower hike on the Little River Trail in the Great Smoky Mountains National Park. I took my Canon 70D, 10-18, 100L Macro, and my iPhone. It was awesome. Great photos of the flowers, the water, and the old vacation homes near the start of the trail. A few years ago, I took the Canon T1i, 15-85mm, 50mm f/1.8 mk II, and the Tamron 18-270 with me to Europe. I won't say regret (Non, je ne regrette rien!), but I learned a lesson: I prefer the 15-85 in the city, I hate switching lenses, and won't take two heavy zooms with me again.
What about you?