It is usually an intuitive choice,
made at the last moment. not impulsive,
mind you, but having to do with how I feel about the subjects,
the conditions, all that.

My normal lunch is an apple and a bit of cheddar.
I suppose the photo corollary would be a Nikon F & 85/1.8,
APX 100 or TMY depending on the moment, or the light.
Xtol/Rodinal/Edwal12, depending on the .... feel.

It's ALWAYS an intuitive choice.