Gaucho (Gottlieb, 1963) JB

Depends...

In most cases I start with the "pen" tool and try to get my lines as close as possible to the appropriate background picture object. When the shape is closed, I start doing the fine adjustment with the "node" tool. I try to keep the number of knots s low as possible to avoid sharp edges in curves (you can still fix this by using the "handles" of the knot, when the curves on both side of the knot are aligned, the knot shape changes from a square into a circle).  Example: if I draw a circle like shape (without using the "circle" tool), I create 4 knots max, the final shape is done by the "node" tool till all four knots change to the circle style. Doing so gives you a smooth line.

I'm using "real" lines only in very few cases, but if id do, I convert them into curves later (Command: "Expand stroke"), then you can aslo adjust the shape. Same for pre-defined objects like squares, circles ets. I also change these into curves (command : "convert to curves).

Another option for lines is to use the "pressure sensitivity" adjustment in the panel "stroke". This gives you many options to manipulate the shape of a basic line. See here: https://affinity.help/designer2/en-US.lproj/index.html?page=pages/Painting/pressure.html&title=Pressure sensitivity

And in some cases, I really draw the lines by hand by using my iPad. On a Mac it's simple. You can add your iPad as additional display, mirror the content of the main screen to it and start drawing with the iPad pen. These "freehand" lines are directly vectors.

I'm sure, there are many more options, but again, I'm pretty new to vector drawing, so I'm using what I described above.

If you have more questons, let me know.