On a full frame body, I have taken an enormous number of portraits over the years, and I can say confidently that 70% or more have been taken with either an 85mm or a 135mm. Like most, I started photography with a 50mm prime and loved it, but I wanted a more cinematic look. I didn’t understand what that meant or really what I was after, until I started to take notice of the lenses other photographers were using and it became clear.
I bought an 85mm next and started using it for headshots and I loved it — I still do. It’s long enough that subject separation is strong, but it’s still wide enough that if you take a few steps back, you can capture more of the scene. Then, after seeing one of my favorite photographers creating stunning images of flowers (of all things!), I invested in a Canon 135mm L and it was my favorite lens until the past few years, but it still sits in second place, miles above third. If there’s good light, it’s hard to take a bad shot with the 135mm wide open, and if you’ve never tried it, I implore you to borrow or rent one to see what it’s like!