On APS-C, the 18-135mm is definitely my most used travel lens and I would pick it as the single one. If APS-C was my only format, I'd potentially replace it with the 16-85mm, because the wide angle is often more useful to me than the long end. But as the KP is my 'compact' travel option (over my K-1), I prefer the less bulky 18-135mm (esp. the hood) and rather complement it with the 15mm Ltd for an overall easier to pack and more versatile combo.
On a recent trip covering Spanish cities and nature with four lenses, out of 1159 pictures, 656 were taken with the 18-135mm and most of the 258mm using with the 40mm Ltd and about 50 of the 152 using the 55-300mm PLM could have adequately been captured with it as well. I only packed the Sigma 8-16mm on a few days (93 exposures), whenever I anticipated interesting wide-angle shots.
The low price (bundled or used) is another advantage of the 18-135mm: I'm on my 3rd at the moment, the first is still going strong as a permanent loan to my daughter despite a lot of (ab-)use, a worn bayonet for the hood and drying mark on the front lens after I took an involuntary swim in a lake. The 2nd was dropped by my son and needs to be repaired for consistent focus but I needed a quick replacement for a trip, so I just bought another used one for a similar amount as the repair, which was available locally.
Last edited by JensE; 12-29-2021 at 09:22 AM.