I have tested an oil based pencil to see how it suits me when drawing croquis.It turns out to work fairly well. I can draw very light lines as well as press down hard for accents. Since it is oil based there is no way to quickly smudge out some areas to describe form.
I also tried an ordinary 2B pencil.
Then I did the drawing in 2B pencil and tried to shift to 9B pencil just for areas to be smudged with the stump. It just did not work and it just felt awkward to shift three times during this short time and I couldnt get a decent shadow in place anyhow.
The last examples is with the soft chalk,the same I used in my first croquis session.
I just love to be able to get real darks when I draw and with the chalk that works. The drawbacks of not getting really light and fine lines with the chalk could be somewhat remedied by developing a lighter touch. Even ordinary lightly applied chalklines appear light in comparison to really heavy darks, so I am prepared to accept this minor drawback.