I got a 50mm Focotar when I bought my Beseler enlarger, and it's been excellent. I've been tempted by faster enlarging lenses like the f/2.8 but focusing is touchy enough even at f/4.5, and trying to actually use the wider aperture would make alignment all the more important. I might find a 40mm useful for making larger enlargments.
I have an EL-Nikkor too, though, the 80mm f/5.6 that has a wide enough field for 6x7 negs, and this also has been very satisfactory. The short focal length is nice for keeping the head reasonably low for enlargements, though it can get a bit tight for small prints.
In extremely careful experiments to see just how good an enlargement from 110 size Verichrome Pan film could be, I got a Minolta 30mm f/2.8 C.E. Rokkor-X enlarging lens. Probably not too much call for one of those now!
But, relating to above comments about using camera lenses for enlarging, I never got a lens specifically for half-frame 35mm negatives, though I've used half-frame quite a bit. Instead, I placed my 8-element 1st version 35mm Summicron on top of an empty Beseler lensboard, set to f/8. This worked surprisingly well, enough that I never shopped for a "proper" enlarging lens for that format.