As an engineer I use pencils quite a lot and like a many engineers I get overly excited by them. I use a variety of thickness and grades depending on what I am doing.
Whilst there is something very tactile and appealing about a nice freshly sharpened traditional wooden pencil I prefer to use an automatic pencil where I can advance the lead for everyday use.
I use a 0.9mm HB Lead for making notes and generally writing things down, a 0.7 F lead for preparing calculations and a 0.5 2H lead for drawing.
The comparison of UK/US pencil grades is:

#0 – 2B
#1 – B
#2 – HB
#3 – H
#4 – 2H

All Wooden pencils with rubbers seem to be HB.