I use different size pens for different projects, but my go-to would have to be the Faber-Castell Pitt Artist Pen! We carry these in several colors. Here's a little about.
What's your "Go To" Pen?
How Do You Use a Dual Brush?
Picking a Pen Brush Size?
I talk through this in my pen pouch demo!
What Are Blendable Pens?
Let me show you!