18-250 for me. It IS the lens I use for 90% or more of my shots at Disney...as well as on any vacation. And it simply does not disappoint - no matter what I have to use it for in a pinch, it can do it...and some things it can do as good as any other lens I've used. To have one lens that can shoot wide, landscape, interior, exterior, wildlife, birds, action, detail, closeup, portrait, and night shots, and which is so compact on the camera as well, makes it simply invaluable.
Of course, I just got back from Disney yesterday where I got to use the Sigma 30mm F1.4 for the first time, and the low light ability of this lens just shone - wonderful lens and lots of Disney fun! And I'd still love to get a wide zoom soon. In the end though, the 18-250 will continue to be the go-to lens when where can be only one.