It is hard to define "Best Travel Lens".
If one knows what you want to photograph, then it is a different story and "Best Travel Lens" do not apply. "Right tools for the right job"
Hence, to me, "Best" in this context means well balance of all the attributes to get a reasonably good photo. (Not needle sharp from center to corner but sharp enough to print 4R or 5R or to view at 1280 pixels length wise). Such include:
1) Ability of reach for commonly used focal lengths (24,28, 35 - 50, 70, 85 and 105)
2) Sharp Center performance wide open and reasonably good corner performance when stopped down to F8
3) Versatility to use hand held in low light (Not going to carry a tripod when walking along the streets overseas or mostly no chance to use tripods when visiting attractions)
4) Compact enough to be attached to body and carry around in a rugsack that contains water bottles and other stuff.
5) Reasonably Light weight as not to fatigue your body when carrying it for the entire day.
If Travel Lens means going on a holiday and photograph what appears in front of you as you are at the destination, then it is best to carry a zoom. (Travelling to photograph a subject would best be done with prior research and bring the best lens in your stash for the task and should not fall into "Travel Lens")
If UWA is required, 16-35mm f/4 VR will fit in very nicely but would be good to carry a 50mm f/1.8 for additional reach. Else the 24-120 f/4 VR will be a good option for more general applications.