So back to the what lens question. For day to day use, I often have a 35mm or 50mm on the camera, and I can see why so many people are attracted to the Voigtländer 40mm f/1.2 and Nikon 40mm f/2; but I am still experimenting on what should be my go to lens in the studio.
I know a number of photographers that have standardised on the 24-105; 24-120mm f/4 and certainly for event photography its a very useful range.
A 180mm can be very pleasing for headshots but not one for regular use.
The 135mm f/1.8 Z lens from Nikon looks stunning but is it too long for studio use. I took my 70-200mm f/2.8 to the studio last month and did a selection of test shots at 135mm to see if its a suitable length for general use. I feel that again like the 180mm, it has a place in your camera bag but not for general study use.
So it looks like the often mentioned 85mm is the lens for me for general studio use.
But sometimes for full length shots or when your shooting in a small space, a 35 or 50mm is needed.
So after all that what to own. If your sensible the 24-120mm f/4 zoom, and a 85mm f/1.2 would seem to suite nine out of ten scenarios, and you might want to add a fast 35mm or small space and lower light work.
So what will be in my bag for studio work, likely a 35, 50, 85 and 135mm, so the 85mm is next on my shopping list as I build out my studio primes.