Best FF lens as a midrange on an APS-C

"Best" is going to vary, for different shooters, but I feel that my 24-105/4L IS is going to remain a work-horse* lens for me, for the foreseeable future, useful on APS-C, APS-H, and full-35mm-frame. Distortion is quite reasonable from 28mm to 105mm, it is at least somewhat weather-sealed, AF is fast and accurate, it has IS, and its MFD allows very close-range shooting, which can be further improved by screwing a 500D onto the filter threads. Being able to zoom to 105mm, rather than just 70mm, is a notable advantage. (For reference, I have a Nikkor 24-70/2.8G, which I use on a D700 camera.)

I disdained mid-range zooms for quite a while, but then added my 24-105L in September 2014, and then the Nikkor 24-70/2.8G in May 2015, and now feel quite differently. I have mostly used the 24-105L on APS-C and APS-H cameras, and have only use the Nikkor 24-70/2.8G on full-35mm-frame.

My EF-S 10-22mm lens complements the 24-105L quite well at the wide end. It is the only EF-S lens I have bought new, and my only other EF-S lens, bought pre-owned, was a brief experiment that I presumed I would trade-away. This lens has notably low distortion, even compared to most wide-angle L lenses. (Until I acquired 7D Mark II cameras, late last year, I could not correct distortion in-camera, and my employer requires OOC JPEGs, with no post-processing allowed.)

A recent addition is my 16-35/2.8L II. While not as trendy and sexy as the more recent 16-35/4L IS, the constant f/2.8 maximum aperture means a 7D Mark II can AF in low light at EV -3. I cannot say my 16-35/2.8L II is a most-favored lens, and I considered selling it quite soon after buying it, but it serves a purpose, starting at wide-normal, and zooming to normal, on APS-C and APS-H cameras. I can correct its distortion in-camera, when shooting with a 7D Mark II.

*I do not claim to be a "professional" photographer, as I am not in the business of photography, and my skill-set is not broadly extensive, but I do shoot some evidentiary/forensic images, primarily in low light, for very important purposes, as part of my duties as a public servant.