My two favourite fountain pens for sketching are

• Green Sailor Fude de Mannen fountain pen with 55 degree ‘bent’ fude nib. This is my most used drawing pen due to the variety of lines I can make by simply changing the angle of the pen. More about it here. I also use the 40 degree Fude but prefer the 55 degree as it creates a thicker line.
• Lamy Joy with a gold nib which is approx medium in size (note: it is not a stub/calligraphy nib which the pen comes with). I love this pen as the body is lightweight, well balanced and just feels so good in my hand. I’m currently using the newer Red and White model. As I use my pen with very light pressure I like a medium nib so I can achieve different thicknesses of line simply by varying how much the nib is touching the page. The gold nib is softer (and a little more flexible) than the normal steel nib.  More about the gold nib in this article – it works for me, but I don’t think that it is worth the cost for most people.

I use generally De Atramentis Document Ink in all my pens. More about ink here.

Check out this article for answers to all the most frequently asked questions about fountain pens.